OBJECTIVE: Inhibin B produced by Sertoli cells may be an important marker of seminiferous tubule function in patients treated with chemotherapy (CT). The aim of this study was to evaluate the inhibin B/FSH ratio to detect male gonadal dysfunction in cancer survivors treated in childhood and adolescence. PATIENTS: Twenty-one male patients (group A) treated with 6-10 courses of CT for Hodgkin's disease during childhood and adolescence were examined 3-11 years after the conclusion of treatment. Twenty healthy young men (18-23 years old) were used as controls (group B). METHODS: Serum samples for the determination of inhibin B, follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone (T), sex hormone-binding globulin (SHBG) and semen for analysis were collected. RESULTS: The median testicular volume of patients of group A was lower than those of group B (p = 0.001) and a positive correlation was found between testicular size and sperm count (r = -0.5, p = 0.01). Semen analysis revealed azoospermia in 11 patients, severe oligospermia in four and normal sperm count in three. No significant difference was found in the median of T, LH, SHBG, inhibin B concentrations and T/LH ratio between the groups. Serum inhibin B was correlated with the serum FSH levels (r = -0.5, p = 0.02). Median FSH was significantly higher (p = 0.0001), and median inhibin B/FSH ratio was significantly lower in group A than in controls (p = 0.0002), but the inhibin B/FSH ratio was higher in the patients with normal sperm count than in those with oligospermia (p = 0.00004). CONCLUSIONS: These results show that the cytotoxic effects of CT cause severe damage to the germinal epithelium with subtle effects on Sertoli cells. To assess Sertoli cell function in men with primary testicular damage after treatment with CT in childhood and adolescence, the inhibin B level needs to be interpreted in the context of the circulating FSH, especially when normal FSH levels are observed.