diff --git a/libraries/stdlib/common/src/kotlin/TextH.kt b/libraries/stdlib/common/src/kotlin/TextH.kt
index c7d8ffc0ab4..5a20077168d 100644
--- a/libraries/stdlib/common/src/kotlin/TextH.kt
+++ b/libraries/stdlib/common/src/kotlin/TextH.kt
@@ -111,8 +111,18 @@ internal expect fun String.nativeLastIndexOf(str: String, fromIndex: Int): Int
 public expect fun String.substring(startIndex: Int): String
 public expect fun String.substring(startIndex: Int, endIndex: Int): String
 
-
+/**
+ * Returns a copy of this string converted to upper case using the rules of the default locale.
+ *
+ * @sample samples.text.Strings.toUpperCase
+ */
 public expect fun String.toUpperCase(): String
+
+/**
+ * Returns a copy of this string converted to lower case using the rules of the default locale.
+ *
+ * @sample samples.text.Strings.toLowerCase
+ */
 public expect fun String.toLowerCase(): String
 public expect fun String.capitalize(): String
 public expect fun String.decapitalize(): String
diff --git a/libraries/stdlib/js/src/kotlin/string.kt b/libraries/stdlib/js/src/kotlin/string.kt
index 3da9cda83ea..bd184ba1840 100644
--- a/libraries/stdlib/js/src/kotlin/string.kt
+++ b/libraries/stdlib/js/src/kotlin/string.kt
@@ -24,10 +24,19 @@ public actual fun String(chars: CharArray, offset: Int, length: Int): String {
     return String(chars.copyOfRange(offset, offset + length))
 }
 
-
+/**
+ * Returns a copy of this string converted to upper case using the rules of the default locale.
+ *
+ * @sample samples.text.Strings.toUpperCase
+ */
 @kotlin.internal.InlineOnly
 public actual inline fun String.toUpperCase(): String = asDynamic().toUpperCase()
 
+/**
+ * Returns a copy of this string converted to lower case using the rules of the default locale.
+ *
+ * @sample samples.text.Strings.toLowerCase
+ */
 @kotlin.internal.InlineOnly
 public actual inline fun String.toLowerCase(): String = asDynamic().toLowerCase()
 
diff --git a/libraries/stdlib/jvm/src/kotlin/text/StringsJVM.kt b/libraries/stdlib/jvm/src/kotlin/text/StringsJVM.kt
index ba001a0e4ca..cf69a4c264b 100644
--- a/libraries/stdlib/jvm/src/kotlin/text/StringsJVM.kt
+++ b/libraries/stdlib/jvm/src/kotlin/text/StringsJVM.kt
@@ -94,12 +94,16 @@ public actual fun String.replaceFirst(oldValue: String, newValue: String, ignore
 
 /**
  * Returns a copy of this string converted to upper case using the rules of the default locale.
+ *
+ * @sample samples.text.Strings.toUpperCase
  */
 @kotlin.internal.InlineOnly
 public actual inline fun String.toUpperCase(): String = (this as java.lang.String).toUpperCase()
 
 /**
  * Returns a copy of this string converted to lower case using the rules of the default locale.
+ *
+ * @sample samples.text.Strings.toLowerCase
  */
 @kotlin.internal.InlineOnly
 public actual inline fun String.toLowerCase(): String = (this as java.lang.String).toLowerCase()
diff --git a/libraries/stdlib/samples/test/samples/text/strings.kt b/libraries/stdlib/samples/test/samples/text/strings.kt
index 79675c04e93..77d9f708d3d 100644
--- a/libraries/stdlib/samples/test/samples/text/strings.kt
+++ b/libraries/stdlib/samples/test/samples/text/strings.kt
@@ -94,4 +94,14 @@ class Strings {
         assertPrints(byteArray.toString(charset), "Hello")
     }
 
+    @Sample
+    fun toLowerCase() {
+        assertPrints("Iced frappé!".toLowerCase(), "iced frappé!")
+    }
+
+    @Sample
+    fun toUpperCase() {
+        assertPrints("Iced frappé!".toUpperCase(), "ICED FRAPPÉ!")
+    }
+
 }