The supposed origin of non-functioning pituitary adenomas (NFPA) from gonadotrophs prompted us to investigate the effects of the gonadotropin-releasing hormone (GnRH) analog nafarelin on hormonal and tumoral parameters in eight patients with NFPA, previously unsuccessfully operated and all hypogonadal. Nafarelin was administered intranasally for 1 year to all patients. Four patients received a dose of 1200 micrograms/day; the remaining four received 800 micrograms/day for 3 months, which was subsequently increased to 1200 micrograms/day. Basal gonadotrophin and alpha-subunit (alpha SU) levels were low-normal. In four patients (nos. 1,2,3,5) nafarelin significantly lowered luteinizing hormone (LH) levels, and also follicle-stimulating hormone (FSH) in three of them (nos. 1,2,3). Persistent FSH stimulation occurred in three patients (nos. 6,7,8), with a transient slight LH increase only in patient no. 8. In one patient (no. 7), alpha SU levels were persistently stimulated. Hormonal responses to an acute GnRH test during nafarelin administration were generally blunted when compared to the pretreatment responses. Immunofluorescence results, obtained before treatment in five adenomas (nos. 2,3,4,6,7), hae been as follows: positive for FSH-beta in all; negative for LH-beta in all, except a few positive cells in case no. 4; positive for alpha SU in three (nos. 2,3,7). No changes of visual field and tumor size occurred in any patient during treatment. However, one patient who showed a persistent increase in FSH levels exhibited left palpebral ptosis after 12 months of therapy and underwent a second transsphenoidal surgery.(ABSTRACT TRUNCATED AT 250 WORDS)