Gonadal function was evaluated in 23 men (aged 14.8\p=n-\28.8 years) treated in childhood with cytotoxic drugs for a solid tumour. Group 1 (N = 14) had been treated with non-alkylating drugs only, while group 2 (N=9) received the alkylating drug cyclophosphamide in addition (range 3.8\p=n-\19.5 g/m2).Median age at the start of treatment was 4.6 years (range 0.6\p=n-\16.1) in group 1 and 13.9 years (range 3.7\p=n-\16.9) in group 2. Data of the patients were compared with a reference group consisting of 14 normal men. Almost all patients of both groups showed normal development of puberty; 13 of the 14 men in group 1 showed normal hormonal values. In group 2, basal LH and FSH as well as the LH and FSH responses to GnRH showed higher levels compared to those of a reference group (p<0.001). Correlation analysis showed an evident correlation between the total dose of received cyclophosphamide and the basal FSH level (r=0.78; p=0.002), the FSH response to GnRH (r=0.73; p=0.002) and the LH response to GnRH (r=0.67; p=0.002). There was no correlation between the hormonal