The effects of an acute stressful and painful stimulus, cold water, on psychomotor and cognitive functioning, was assessed in 14 healthy volunteers. Subjects immersed their forearm in ice-cold water (2-3 degrees C) and luke-warm water (37 degrees C) for 3 min, and during this time period a psychomotor or cognitive test was performed. These immersions were done over the course of two experimental sessions, spaced at least 2 days apart, with six trials in each session. Within each session, cold and warm water immersions alternated. Results indicated that flicker-from-fusion threshold from the critical flicker frequency test was higher in the cold-water condition than in the luke-warm-water condition, indicative of increased alertness from the cold stimulus. Short-term memory was attenuated, however, in the cold-water condition. Performance on other tests including those that required speed and/or concentration were not affected by the manipulation. Subjects rated the cold-water stimulus as painful and bothersome, and their blood pressure was significantly elevated by the stimulus. We conclude that a painful stimulus may affect psychomotor and/or cognitive functioning, but the relationship is somewhat complex and depends on the particular tests used.