The cognitive processes at work in masked priming experiments are usually considered automatic and independent of attention. We provide evidence against this view. Three behavioral experiments demonstrate that the occurrence of unconscious priming in a number comparison task is determined by the allocation of temporal attention to the time window during which the prime-target pair is presented. Both response-congruity priming and physical repetition priming vanish when temporal attention is focused away from this time window. These findings are inconsistent with the concept of a purely automatic spreading of activation during masked priming.