Single unit activity was recorded from the prefrontal cortex (principalis, arcuate and inferior convexity areas) of the monkey while the animal was performing a delayed conditional discrimination task. Sequential events of the task were as follows: instructional cue presentation, 1st delay, presentation of two pattern stimuli on left and right windows respectively as a discriminative cue, 2nd delay and choice response to the left or right window. The positive pattern was dependent on the instructional cue. In total, 424 units obtained from two monkeys showed a correlation with some aspects of the task. Of these 424 task-related units, 169 differential between the instructional cues and/or the discriminative cues. The majority of these differential units (n = 123) were found to be related to spatial information processing (related to the side of the response) while 19 differential units were related to non-spatial information processing (related to the color or pattern configuration of the cue). The activity of the remaining 27 differential units was considered to be related to both spatial and non-spatial information processing (related to both the instructional cue and the side of the response) and this type of unit was shown to be involved in conditional information processing. The results indicate that prefrontal units may be related to the meaning of the stimulus independent of its physical properties.