We studied 24 male patients aged 26-62 years (median 41) prospectively presenting over a 5 year period with clinical features of hypogonadism and erectile dysfunction (ED), who had been treated with autologous or allogeneic bone marrow/stem cell transplant for a variety of haematological malignancies and had received either high-dose chemotherapy or high-dose chemotherapy combined with total body irradiation (TBI). Ten healthy adult controls (aged 35-50 years) were also studied. Erectile dysfunction (ED) was assessed clinically and by colour flow Doppler studies of the cavernosal vessels. Testicular function was assessed by testicular volume including orchidometry, FSH, LH and testosterone measurements. Libido and ejaculatory function were also recorded. Patients had severe hypogonadism as evidenced by low mean testicular volume (7.0 +/- 2.4 ml vs 20 +/- 2.0 ml; P < 0.001), elevated gonadotrophins (FSH = 18.54 +/- 7.61 vs 5 IU/l (P < 0.001); LH = 8.02 +/- 2.89 vs 3. 9 IU/l (P < 0.001)) and low normal mean testosterone levels (16.4 nmol/l +/- 9.1 vs 22.4 nmol/l (P < 0.5)). Cavernosal arterial insufficiency was found in 11/14 of TBI-treated and in 3/10 HDC-treated patients, indicative of vasculogenic damage to corpora cavernosal vessels. Patients were given a therapeutic trial with testosterone replacement therapy (TRT). Those who had diminished libido had a marked improvement in their symptoms but the effect of TRT on ED was equivocal. In conclusion, this is the first report to show vasculogenic insufficiency in patients with haematological malignancies treated by BMT. Although hypogonadism can account for diminished libido, arteriogenic insufficiency is likely to be an important factor accounting for ED in these patients, especially those treated by TBI. We recommend a comprehensive assessment including endocrine profile and colour flow Doppler study in formulating the best management plan in recipients of high-dose therapy presenting after transplant with ED.