Sleep staging was performed on 32 patients with infantile spasms. All patients demonstrated significantly less total sleep time and lower percentage of REM time than the expected normal values for age. Seventeen were treated with ACTH or prednisone. There was no increase in total sleep time in those who received hormone therapy, whether or not it was successful. However, the percentage of REM time increased significantly in patients who responded to therapy; this increase occurred concurrently with clinical and electroencephalographic improvement. There was no significant change in REM-sleep values in patients who did not respond.