Post-trial unit activity was examined in the prefrontal cortex (PFC) of the monkey during a Go/No-go (symmetrical reinforcement) discrimination task. Among 219 units which showed post-trial activity changes (reward-related, reinforcement-related, error-related, reinforcement-error-related and end-of-trial-related), 25 units responded differentially to the juice reward after different behavioral responses (Go and No-go). Seven units coded the 'correctness' of the response apart from the presence or absence of the reward. The results implicate the PFC in cognitive functions related to the coding of post-trial events.