Abstract
In three trials conducted by the Medical Research Council on acute lymphoblastic leukaemia in childhood the incidence of testicular infiltration in relation to presenting features and treatment was analysed. Initial severe thrombocytopenia was associated with an increased incidence. Testicular infiltration was occasionally found during treatment in patients with high blood leucocyte counts at diagnosis but the main incidence in patients with all types of disease occurred within one year of stopping treatment. The incidence may be increased when "second-line" drugs, especially cyclophosphamide, have been used. A reappraisal of the value of additional drugs in maintenance treatment of patients with good prognosis is needed.