Oestradiol (Oe2), testosterone (T), lutenizing hormone (LH), follicle stimulating hormone (FSH), beta-human chorionic gonadotrophin (beta-hCG) and alpha-1 foetoprotein (AFP) were measured in blood samples taken from 63 patients with testicular tumours. In patients without tumour recurrence (n=31) AFP, Oe2 and T were within the normal range, beta-hCG was negative, LH levels were marginally elevated and FSH concentrations were significantly elevated. In patients with tumor recurrence (n=32) Oe2 was significantly elevated, whereas the T levels varied considerably and were therefore statistically not different from the patients without tumour recurrence. The beta-hCG positive subgroup of the recurrence group, however, demonstrated significantly elevated T levels. T levels were highest in patients with 51 to 500 U beta-hCG/1. On hand T was normal or even low normal in beta-hCG negative -AFP positive patients. In all subgroups decreasing FSH levels and decreasing LH responses to LRH were among the earliest signs of tumour recurrence. The observations suggest that moderate hCG levels are able to stimulate testicular T production, whereas high levels no longer increase T serum concentrations. Increased conversion rates form steroid precursors to oestradiol seem to be a feature of beta-hCG positive as well as beta-hCG negative testicular tumours.