The behavioral relationships of 396 striatum neurons with regular, tonically elevated discharge rates were studied. While monkeys performed a delayed gonogo task, neurons predominantly located in medial putamen responded with phasic depressions (n = 30) or activations (n = 5) to task-specific stimuli. Particularly effective was an instruction light preparing for movement or no-movement reactions, and an auditory signal associated with reward delivery. Stimuli triggering arm or mouth movements were less effective. The data demonstrate that these usually poorly modulated neurons display context-dependent phasic activity in specific behavioral situations.