diff --git a/README.md b/README.md
index b5f4250..c2ad3b3 100644
--- a/README.md
+++ b/README.md
@@ -194,6 +194,15 @@ By default, literal matching is performed. The assertion fails if
 }
 ```
 
+The expected output can be specified with a heredoc or standard input as well.
+
+```bash
+@test 'assert_output() with pipe' {
+  run echo 'have'
+  echo 'want' | assert_output
+}
+```
+
 On failure, the expected and actual output are displayed.
 
 ```
@@ -283,6 +292,15 @@ By default, literal matching is performed. The assertion fails if
 }
 ```
 
+-The unexpected output can be specified with a heredoc or standard input as well.
+
+```bash
+@test 'refute_output() with pipe' {
+  run echo 'want'
+  echo 'want' | refute_output
+}
+```
+
 On failure, the output is displayed.
 
 ```
diff --git a/src/assert.bash b/src/assert.bash
index 2e8015e..b2d1d2c 100644
--- a/src/assert.bash
+++ b/src/assert.bash
@@ -10,7 +10,7 @@
 #
 # You should have received a copy of the CC0 Public Domain Dedication
 # along with this software. If not, see
-# <http://creativecommons.org/publicdomain/zero/1.0/>. 
+# <http://creativecommons.org/publicdomain/zero/1.0/>.
 #
 
 #
@@ -165,7 +165,8 @@ assert_failure() {
 }
 
 # Fail and display details if `$output' does not match the expected
-# output.
+# output. The expected output can be specified either by the first
+# parameter or on the standard input.
 #
 # By default, literal matching is performed. The assertion fails if the
 # expected output does not equal `$output'. Details include both values.
@@ -186,10 +187,12 @@ assert_failure() {
 #   -p, --partial - partial matching
 #   -e, --regexp - extended regular expression matching
 # Arguments:
-#   $1 - expected output
+#   $1 - [=STDIN] expected output
 # Returns:
 #   0 - expected matches the actual output
 #   1 - otherwise
+# Inputs:
+#   STDIN - [=$1] expected output
 # Outputs:
 #   STDERR - details, on failure
 #            error message, on error
@@ -215,7 +218,8 @@ assert_output() {
   fi
 
   # Arguments.
-  local -r expected="$1"
+  local expected
+  (( $# == 0 )) && expected="$(cat -)" || expected="$1"
 
   # Matching.
   if (( is_mode_regexp )); then
@@ -252,6 +256,8 @@ assert_output() {
 }
 
 # Fail and display details if `$output' matches the unexpected output.
+# The unexpected output can be specified either by the first parameter
+# or on the standard input.
 #
 # By default, literal matching is performed. The assertion fails if the
 # unexpected output equals `$output'. Details include `$output'.
@@ -274,10 +280,12 @@ assert_output() {
 #   -p, --partial - partial matching
 #   -e, --regexp - extended regular expression matching
 # Arguments:
-#   $1 - unexpected output
+#   $1 - [=STDIN] unexpected output
 # Returns:
 #   0 - unexpected matches the actual output
 #   1 - otherwise
+# Inputs:
+#   STDIN - [=$1] unexpected output
 # Outputs:
 #   STDERR - details, on failure
 #            error message, on error
@@ -303,7 +311,8 @@ refute_output() {
   fi
 
   # Arguments.
-  local -r unexpected="$1"
+  local unexpected
+  (( $# == 0 )) && unexpected="$(cat -)" || unexpected="$1"
 
   if (( is_mode_regexp == 1 )) && [[ '' =~ $unexpected ]] || (( $? == 2 )); then
     echo "Invalid extended regular expression: \`$unexpected'" \
diff --git a/test/50-assert-15-assert_output.bats b/test/50-assert-15-assert_output.bats
index 2c6b750..de622f5 100755
--- a/test/50-assert-15-assert_output.bats
+++ b/test/50-assert-15-assert_output.bats
@@ -26,6 +26,16 @@ load test_helper
   [ "${lines[3]}" == '--' ]
 }
 
+@test 'assert_output(): reads <expected> from STDIN' {
+  run echo 'a'
+  run assert_output <<STDIN
+a
+STDIN
+echo "$output"
+  [ "$status" -eq 0 ]
+  [ "${#lines[@]}" -eq 0 ]
+}
+
 # Output formatting
 @test "assert_output() <expected>: displays details in multi-line format if \`\$output' is longer than one line" {
   run printf 'b 0\nb 1'
diff --git a/test/50-assert-16-refute_output.bats b/test/50-assert-16-refute_output.bats
index db7e6ed..2d47155 100755
--- a/test/50-assert-16-refute_output.bats
+++ b/test/50-assert-16-refute_output.bats
@@ -25,6 +25,15 @@ load test_helper
   [ "${lines[2]}" == '--' ]
 }
 
+@test 'refute_output(): reads <unexpected> from STDIN' {
+  run echo 'a'
+  run refute_output <<INPUT
+b
+INPUT
+  [ "$status" -eq 0 ]
+  [ "${#lines[@]}" -eq 0 ]
+}
+
 # Output formatting
 @test 'refute_output() <unexpected>: displays details in multi-line format if necessary' {
   run printf 'a 0\na 1'