The cause of autism is unknown. Recently, it has been suggested that it involves metabolic disorders of serotonin and/or dopamine. On the other hand, there is a close relationship between hormone secretion and monoamines. The aim of this study was to analyze the secretion of GH, PRL, TSH, cortisol, LH and FSH. The subjects were 30 children with autism, 25 males and 5 females, aged from 1 10/12 to 9 10/12 years. Their IQs (DQs) ranged from 34 to 123. Pituitary hormone secretion was measured during provocation with insulin (0.1 unit/kg), TRH (10 micrograms/kg) and/or LH-RH (100 micrograms/m2) in 26 of 30 cases. Control subjects included 16 age-matched children with attention deficit disorder (ADD) and 18 age-matched children with mental retardation (MR) without autistic and organic central nervous diseases. The 24-hour secretion rhythm of GH, PRL and cortisol for 14 cases with autism and of LH and FSH for 9 cases was also investigated. In insulin provocation test, the peak values of GH and delta GH (peak GH level minus baseline GH level) in ADD were significantly higher than those in MR (p less than 0.05). In TRH provocation test, the peak values of TSH and delta TSH in autism were significantly lower than those in MR. Five cases of autistic children revealed borderline responses for TSH, while the only one each of ADDs and MRs revealed borderline responses for TSH. In a study of the 24-hour hormone secretion rhythm, eleven of the 14 autistic children showed an abnormal secretion rhythm.(ABSTRACT TRUNCATED AT 250 WORDS)