Thirty-three acromegalic patients were treated with radiotherapy and followed up for at least 3 years (mean 6 years, range 3 to 12). Seventeen had not had previous pituitary ablative therapy and 16 had. The mean GH level for these two groups before radiotherapy was comparable at 98 and 119 mIU/l. The observed frequency of reaching < 10 mIU/l was 53% and 75% of patients in the two groups, respectively, the mean observed falls in growth hormone level were 81 and 85% of the initial level, and the calculated exponential decline rate of GH level was 72 and 52% per year. Considering all 35 patients, requirement for pituitary hormone replacement therapy increased from 15 patients before radiotherapy to 20 after radiotherapy, being mostly those who had had prior ablative therapies. There were no complications attributable to the radiotherapy treatment. It appears that radiotherapy is equally efficacious whether a prior unsuccessful ablative procedure had been used or not.