With the increasing cure rate of patients treated for Hodgkin's and non-Hodgkin's lymphoma, the evaluation of late effects on gonadal function remains an important issue. The gonadal function of relapse-free long-term survivors with high-grade non-Hodgkin's lymphoma (NHL) and Hodgkin's disease (HD) were studied; 24 of 119 patients with NHL treated between 1980 and 1990 and 66 of 364 patients with HD treated between 1975 and 1990 at Hannover University Medical School, who were younger than 45 years of age and in complete remission at the time of evaluation for at least 24 months after completion of therapy, were included into the analysis. Of 24 patients with NHL, 1/10 women (10%) and only 3/14 men (21%) showed signs of gonadal dysfunction. Three of these four patients had been treated with combined modality therapy followed by maintenance COP chemotherapy, resulting in high cumulative doses of cyclophosphamide (range: 12–43 g). In comparison, 13/26 (50%) women with HD suffered from premature ovarian failure, and 26/40 (65%) men showed signs of gonadal dysfunction with significant FSH elevations. No significant difference in the incidence of gonadal toxicity existed in patients treated with combined modality who received irradiation to either supra- or infradiaphragmatic radiation fields in combination with chemotherapy (70% versus 62%). A comparison of the chemotherapy regimens used in patients with NHL or HD shows that patients from both groups had received comparable median cumulative doses of cyclophosphamide, vincristine, and adriamycin, but only patients with HD had additionally received a median cumulative dose of 13.3 g of procarbazine per patient. A tendency towards a higher incidence of gonadal toxicity with higher cumulative doses of procarbazine received was found in patients with HD. The frequency of gonadal dysfunctions is markedly lower in patients treated for non-Hodgkin's lymphoma than in patients treated for Hodgkin's disease, approximately half of whom will be affected by long-term gonadal toxicity. Although the use of more intensive radiotherapy in patients with HD compared with NHL patients makes the evaluation of the influence of radiotherapy on gonadal toxicity more difficult, the current retrospective analysis raises the concern that, in addition to infradiaphragmatic radiotherapy, the use of procarbazine in regimens for the treatment of HD, like COPP or MOPP, may be a possible explanation for the differences in gonadal toxicity observed between patients with HD and those with NHL. Regimens including procarbazine should be avoided in patients wanting to preserve fertility since alternative chemotherapies with at least equal efficacy are available.