A battery of computerised tests and the classical Stroop test were administered to a group of 56 patients with DSM-III-R schizophrenia and 17 controls to explore the nature of the mental processes associated with the psychomotor poverty and disorganisation syndromes. In patients with persistent illness, psychomotor poverty was associated with slower responses in a two-choice guessing task in which the appropriate response was not dictated by the circumstances. This association was not observed in patients with remitting illness, providing neuropsychological support to the distinction between 'negative' and 'deficit' symptoms in schizophrenia. Disorganisation syndrome was associated with impaired performance in the classical Stroop test, as shown in previous studies, but not with impairment in a task which required suppression of processing of irrelevant aspects of a stimulus, nor with impairment in a task which required the suppressing of a primed but irrelevant non-verbal response. This suggests that the disorganisation syndrome might be associated with a specific difficulty in suppressing irrelevant verbal responses.