Summary Fatigue, sexual dysfunction, anxiety and depression are all more common in patients who have previously been treated with cytotoxic chemotherapy and radiotherapy (XRT) for haematological malignancies. Following therapy, a significant proportion of men have biochemical evidence of Leydig cell dysfunction, defined by a raised luteinizing hormone level in the presence of a low/normal testosterone level. We postulated that mild testosterone deficiency may account for some of the long-term side-effects of treatment, and we have therefore assessed fatigue, mood and sexual function by questionnaire in 36 patients with Leydig cell dysfunction (group 1), and also in a group of 30 patients (group 2) with normal hormone levels who underwent the same treatment for cancer. There was no significant difference in anxiety and depression scores between the two groups although anxiety scores were higher than those previously reported for normal men. Eightyseven per cent of group 2 were sexually active compared with only 69% of group 1 (P = 0.1), and patients in group 1 engaged less in sexual activity than those in group 2 (mean of 1.8 times per week compared with 3.2 times per week; P = 0.02) Fatigue scores were significantly higher in both groups compared with normal men, but there were no significant differences in any of the fatigue subscales between the two groups. We conclude that mild Leydig cell insufficiency following treatment with cytotoxic chemotherapy ± XRT is not associated with higher levels of fatigue and anxiety but may result in reduced sexual function. These results do not provide a convincing argument that androgen replacement therapy is mandatory to improve quality of life in the majority of these patients, although it may be beneficial in a minority. To establish criteria for selection of patients for a trial of androgen therapy a randomized placebo-controlled study will be necessary.