Drive stimulus in-tensity for rats was manipulated by means of water temperature in a straight-alley tank, and reinforcement was manipulated independently by means of the differential temperature between the alley tank and a separate goal tank. Several studies are reported indicating that reinforcement is a major determinant of behavior in this escape conditioning situation. Drive stimulus intensity, on the other hand, apparently only has a differential effect at very high levels. Several advantages with this technique are pointed out including the fact that speed of swimming per se does not vary with training.