diff --git a/doc/ctype.txt b/doc/ctype.txt
index c7c686f..162ef5f 100644
--- a/doc/ctype.txt
+++ b/doc/ctype.txt
@@ -20,6 +20,14 @@ The following functions are defined:
                       Note: Calls internal routine isaln, which in turn
                       calls internal routines isdgt and isalp.
                       
+  b = isalnu(c);      Returns TRUE if c is an alphanumunder, otherwise FALSE.
+                      
+                      An alphanumunder character is a letter (A-Z or a-z), 
+                      a digit (0-9), or an underline (_). 
+                     
+                      Note: Calls internal routine isalu, which in turn
+                      calls internal routines isdgt and isalp.
+                      
   b = isalph(c);      Returns TRUE if c is alphabetic, otherwise FALSE.
                       
                       An alphabetic character is a letter (A-Z or a-z). 
@@ -116,6 +124,6 @@ Implementation: The standard method of implementing the ctype library is to
 use a bit mask table of 128 bytes (one for each standard ASCII character).
 
 This library instead uses a series of comparisons in the internal routines,
-which leave the accumulator unmodified, and occupies approximately 128 bytes 
-of memory.
+which leave the accumulator unmodified, and generates approximately 128 bytes 
+of machine code.
 
diff --git a/include/ctype.a02 b/include/ctype.a02
index 1304d76..2fe64d0 100644
--- a/include/ctype.a02
+++ b/include/ctype.a02
@@ -11,6 +11,8 @@
         SUBROUTINE CTYPE
 
 ;Character Test Functions - Set Accumulator
+ISALNU: JSR ISANU   ;Is Alphanumunder
+        BVC .ISBTF
 ISALNM: JSR ISALN   ;Is Alphanumeric Character
         BVC .ISBTF
 ISALPH: JSR ISALP   ;Is Alphabetic Character
@@ -55,10 +57,13 @@ TOUPPR: JSR ISLWR   ;If Char IS Not Lower Case
         RTS         ; and Return
 
 ;Machine Language Subroutines - Set/Clear Carry, Preserve Accumulator 
-ISALN:  JSR ISDGT  ;If Char IS Digit
+ISANU:  CMP #$5F    ;If Char = '_'
+        BEQ .ISSEC  ;  Return Carry Set
+                    ;Else
+ISALN:  JSR ISDGT   ;If Char IS Digit
         BCS .ISRTS  ;  Return Carry Set
                     ;Else
-ISALP:  JSR ISUPR  ;If Char IS Upper Case
+ISALP:  JSR ISUPR   ;If Char IS Upper Case
         BCS .ISRTS  ;  Return Carry Set
                     ;Else
 ISLWR:  CMP #$61    ;If Char < 'a'
diff --git a/include/ctype.h02 b/include/ctype.h02
index ba908b4..49e4bf4 100644
--- a/include/ctype.h02
+++ b/include/ctype.h02
@@ -8,6 +8,12 @@
  * Returns: TRUE or FALSE           */
 char isalnm();
 
+/* Check for Alphanumunder Character *
+ *   (Alphabetic, Digit, or '_')     *
+ * Args: c - Character to Check      *
+ * Returns: TRUE or FALSE            */
+char isalnu();
+
 /* Checks for Alphabetic Character  *
  *   (Upper Case or Lower Case)     *
  * Args: c - Character to Check     *
diff --git a/test/ctypetst.c02 b/test/ctypetst.c02
index 2ab68a2..49a3e79 100644
--- a/test/ctypetst.c02
+++ b/test/ctypetst.c02
@@ -21,6 +21,7 @@ head:
   putchr('L'); //Lower Case  
   putchr('A'); //Alphabetic
   putchr('N'); //Alphanumeric
+  putchr('M'); //Alphanumunder
   putchr('G'); //Graphic
   putchr('R'); //Printable
   putchr('B'); //Binary
@@ -43,6 +44,7 @@ loop:
   c = islowr(i) & $0A | $20; putchr(c);
   c = isalph(i) & $0A | $20; putchr(c);
   c = isalnm(i) & $0A | $20; putchr(c);
+  c = isalnu(i) & $0A | $20; putchr(c);
   c = isgrph(i) & $0A | $20; putchr(c);
   c = isprnt(i) & $0A | $20; putchr(c);
   c = isbdgt(i) & $0A | $20; putchr(c);
@@ -51,6 +53,6 @@ loop:
   if (i == 0) goto exit;
   if (i & $0F <> 0) goto loop;
   newlin();
-  c = getkey(); 
+  c = getchr(); 
   if (c == $1B) goto exit;
   goto head;