The use of thin-layer immunoassay (TIA) for the detection of opiates in postmortem blood samples has been developed. Samples required no preparation other than protein removal, which was accomplished easily by the use of a commercially available ultrafiltration device. The procedure was evaluated in a blind study of 82 postmortem blood samples and found to be reliable. Opiate was detected in these samples at a RIA-determined concentration as low as 10 ng/mL.