Recent reports indicate that rats acutely stressed by inescapable footshock, rotation, restraint, or injections of hypertonic saline display increased tail-flick latencies. The present study parametrically analyzed the time course of analgesia following exposure to another stressor, a brief, forced cold water swim, by means of three nociceptive reflex tests. Rats acutely subjected to a cold water (2°C) swim for 3.5 min displayed significantly elevated tail-pinch and flinch-jump thresholds for up to 60 min; no change was noted in similarly treated warm water (28°C) controls. Tail-flick withdrawal latencies to radiant heat stimuli exhibited similar, but more enduring, increases, lasting up to 120 min. These results demonstrate that reactivity to three different nociceptive reflex modalities, electric shock, heat, and pressure, can be altered by acute exposure to a stressor.