It is essential that nurses gain insight about the responses of older adults to standard anticancer therapies because there is ongoing concern about whether the elderly are affected adversely by the prescribed therapy. The purpose of this longitudinal prospective study was to describe selected outcomes and their relationships in a sample of 45 elderly (mean age 69.8 years; range 61-86) patients receiving radiotherapy for either breast (42%) or lung (58%) cancer. The outcome variables were weight and multidimensional functional status; moderator variables were co-morbidity, nutritional intake, estimated adequacy of intake, radiation dose, side effects, and social support. Data were collected at the beginning of radiation (T1), the middle of therapy (T2), the conclusion of therapy (T3), and three months post radiation (T4). Although 81.4% had some concurrent condition, those with a comorbid condition did not respond significantly differently from those without a comorbid condition on any of the major variables at any of the four times. At none of the four times was the caloric intake adequate to meet the estimated energy requirements for usual activity (range 67.9-71.5%). However, caloric intake was not significantly related to weight at any of the four times. There was a significant weight decrease from beginning of therapy to the middle of therapy and from the beginning of therapy to conclusion of therapy. The percentage of calories contributed by protein was significantly correlated with weight during radiotherapy, and protein calories consumed at the previous time were correlated with weight at T2 and T3. In contrast, the percentage of calories contributed by carbohydrate intake was significantly negatively correlated with two of the four functional status measures at each time, but was not related to weight. In addition carbohydrate calories consumed at the previous time also were related to one or more functional status measures at succeeding time points. Almost no relationships were found between social support and the outcome measures of weight and functional status. Scores on three of the four functional status measures suggest improvement over time from initiation of radiation to 3 months after therapy. Scores on the fourth measure, Overall Health Rating, suggest a slight decline; however, the average score reflects good overall health. These findings provide evidence that this group of elderly, the great majority of whom had at least one comorbid condition, tolerated the course of radiation with less than adequate intake for usual activity, a slight decrease in mean weight, but without major disruptions in functional status.(ABSTRACT TRUNCATED AT 400 WORDS)