The distribution of hexamethylmelamine (HMM) was investigated in surgical biopsies from 12 patients with pelvic cancer who were given an oral dose of 200 mg at 2-24 hours before the operation. The highest concentrations of HMM were found in tissues, such as omentum and subcutaneous tissue, that have a predominant lipidic component. HMM concentrations in the primary tumor were lower than in other tissues and were similar to those in plasma. HMM concentrations in metastases appeared to be higher than in the primary tumor, and in metastases with a diameter less than 3 mm, drug levels were two to ten times those in larger ones. Plotting the HMM concentrations versus time, utilizing the data from different patients, the elimination half-lives were found to be 9.05, 8.82, and 8.53 in plasma, tumor, and subcutaneous tissue, respectively.