Changes in dietary intake, nutritional status, body composition and well-being were studied in 108 cancer patients over a period of 20 weeks. The patients, constituting a group of elderly women with uterine cancer, a group of elderly men with urological cancer and a group of male and female patients of various ages with malignant lymphoma, were prospectively followed during and after aggressive treatment given with curative intent. Detailed information on the dietary intake was measured by a dietary history and cross-check method covering the 2 months prior to the onset of therapy and a 48-hr dietary record which was applied seven times during the observation period. The nutritional status was monitored by anthropometric measurements and laboratory assays in blood and urine. The patient's well-being was assessed by the use of standard performance scales by the observers and the application of patient's questionnaires concerning complaints, ability to self-care, mobility and daily activities. The main results are described here, indicating that: (1) most patients studied had a more than adequate diet during the 2 months preceding cancer therapy when compared to the Dutch Recommended Dietary Allowances; (2) the impact on dietary intake and nutritional status was relatively minor and generally transient; and (3) the treatment course was accompanied by distinct changes of well-being associated with, but not necessarily resulting from or leading to, changes of dietary intake.