Stress in the rat has been reported to enhance the analgesic and thermic effects of opioids, drug effects that are mediated centrally. We examined whether this stress-induced enhancement of response to opioids could also be demonstrated for a drug effect mediated largely in the periphery, morphine-induced inhibition of gastrointestinal transit. Restrained (stressed) and unrestrained (unstressed) rats were injected with saline or morphine and then administered orally a charcoal suspension; after sacrifice, the distance the charcoal traveled through the intestine was determined. After the administration of saline, restrained rats had significantly lower gastrointestinal transit than did unstressed rats; however, both groups were comparably sensitive to inhibition of gastrointestinal transit by morphine.