Succinylcholine, a short-acting muscle relaxant, has been reported as the cause of prolonged apnea following administration to some surgical patients. A relationship between increased sensitivity to succinylcholine and decreased levels of pseudocholinesterase has been established. This study uses a manual adaptation of an automated method to screen surgical patients for pseudocholinesterase activity in an effort to determine the frequency of abnormally low levels and their relationship to surgical complications. The results suggest that a routine screening program for surgical succinylcholine candidates should be considered.