The food intake was analysed by means of a 3-day diary in 35 patients with cystic fibrosis, aged 1-65 years. All patients were prescribed an ordinary diet, and all had normal height and weight. The reliability of the method was checked in two patients, who kept diaries twice during a 6-month period. The results were almost identical. Most patients had a satisfactory intake of calories (mean (+/- SD) 97 +/- 23%). Only in five cases was the intake of calories per kg body weight less than that recommended. Protein constituted 11-22 kcal%, the mean protein intake being 178 +/- 55% of the recommended dietary allowance (RDA), most patients having much higher amount per kg body weight than that recommended. The mean fat content of the diet was 37 +/- 6 kcal% (range, 24-59). The calcium was in most cases much more than recommended owing to a high milk intake, the mean intake of calcium being 177 +/- 72% of RDA (range, 89-350). One additional patient had an extremely unbalanced diet, resulting in a caloric intake of more than 300% of RDA. This was due to supplementation with large amounts of special carbohydrate solutions (doctor's prescription), constituting 78 kcal%. Patients with cystic fibrosis on a free normal diet seem to have a satisfactory caloric intake compared with healthy individuals. The protein intake was too high, similar to what hsa been found in healthy Swedish children. The implication of this protein load in a disease with kidney and liver involvement has to be considered.(ABSTRACT TRUNCATED AT 250 WORDS)