Prolactin, FSH, LH and TSH were determined in repeated samples of serum from 16 unmedicated male patients with chronic schizophrenia. Changes in the mental states between the 2 occasions were related to changes in hormone levels. Significant inverse correlations were established between prolactin and incoherence of speech, between prolactin and total positive symptoms and between FSH and poverty of speech. A significant positive correlation was established between FSH and delusions. These findings are discussed in the context of evidence concerning the role of monoamines in the control of anterior pituitary function, and of the dopamine and other monoamine hypotheses of schizophrenia. Although prolactin secretion was not as low, as would be predicted on the basis of the dopamine overactivity hypothesis of schizophrenia, the relationship between symptom change and change in prolactin secretion was consistent with the hypothesis that increasing symptom severity is associated with increasing dopamine release from the tubero-infundibular system.