The activity of premotor cortex neurons was studied in macaque monkeys that were operantly conditioned to perform a visually guided motor task. The monkeys were given a visuospatial instruction stimulus (IS) that provided the target for a limb movement, but the monkey was not allowed to execute the movement until the later presentation of a trigger stimulus (TS). The IS was sometimes removed or the target changed during the interval between the IS and TS. Certain neurons became active before the IS, appearing to anticipate its location or time of occurrence, some of these and other neurons increased or decreased their discharge prior to a possible change in the IS, and other cells showed neuronal modulation that preceded the TS. The properties of some of these neurons were examined when the timing of the behavior-guiding visual signals or their probability of occurrence was made less predictable. In general, the neuronal activity described here was strongly influenced by changes in event predictability. These findings suggest that neuronal activity within the premotor cortex reflects the anticipation of predictable environmental events.