diff --git a/lib/core_lib.sh b/lib/core_lib.sh
index 2c18d6c..3c2dcc7 100755
--- a/lib/core_lib.sh
+++ b/lib/core_lib.sh
@@ -174,7 +174,7 @@ make_temp_file () {
 # Prints a message to a log file.
 #
 # Usage:
-#   $ print_log_message LOG_MESSAGE LOG_FILE
+#   $ print_log_message [-DWIE] LOG_MESSAGE LOG_FILE
 #
 # Computes a timestamp and prepends the timestamp to the message
 # before appending the message to the log file.
@@ -185,11 +185,46 @@ make_temp_file () {
 print_log_message () {
 
 	# local vars
+	local prefix
 	local log_message
 	local log_file
 	local tstamp
+
+	local opt
+	local OPTARG
+	local OPTIND
+	while getopts ":DWIE" opt; do
+		case $opt in
+			D)
+				prefix=DEBUG
+				;;
+			W)
+				prefix=WARN
+				;;
+			I)
+				prefix=INFO
+				;;
+			E)
+				prefix=ERROR
+				;;
+			\?)
+				echo "ERROR: $FUNCNAME: Unrecognized option: -$OPTARG" >&2
+				return 2
+				;;
+			:)
+				echo "ERROR: $FUNCNAME: Option -$OPTARG requires an argument" >&2
+				return 2
+				;;
+		esac
+	done
+	
+	# default to INFO
+	if [ -z "$prefix" ]; then
+		prefix=INFO
+	fi
 	
 	# make sure there are two command-line arguments
+	shift $(( OPTIND - 1 ))
 	if [ $# -ne 2 ]; then
 		echo "ERROR: $FUNCNAME: incorrect number of arguments: $# (2 required)" >&2
 		return 2
@@ -203,7 +238,7 @@ print_log_message () {
 	tstamp=$( /bin/date -u +%Y-%m-%dT%TZ )
 	
 	# prepend timestamp to the log message
-	printf "%s %s\n" "$tstamp" "$log_message" >> "$log_file"
+	printf "%s %s %s\n" "$tstamp" "$prefix" "$log_message" >> "$log_file"
 }
 
 #######################################################################
diff --git a/lib/http_tools.sh b/lib/http_tools.sh
index a8fdcb6..c4f08fe 100755
--- a/lib/http_tools.sh
+++ b/lib/http_tools.sh
@@ -247,7 +247,7 @@ conditional_get () {
 		
 		# quiet failure mode
 		if $cache_only_mode; then
-			print_log_message "$FUNCNAME: ERROR: resource not cached: $location" "$log_file"
+			print_log_message -E "$FUNCNAME: resource not cached: $location" "$log_file"
 			return 1
 		fi
 		
@@ -403,7 +403,7 @@ conditional_get () {
 	elif [ "$response_code" = "304" ]; then
 		# quiet failure mode
 		if $force_output_mode; then
-			print_log_message "$FUNCNAME: ERROR: resource not modified: $location" "$log_file"
+			print_log_message -E "$FUNCNAME: resource not modified: $location" "$log_file"
 			return 1
 		fi