Type I collagen synthesis was studied in 12 female Wistar rats weighing 60 +/- 5 g at the beginning of the experiment. The animals were fasted for 24 h and then injected ip with 10-mu-Ci uniformly labeled [C-14]-glycine. Two hours later, groups of 4 animals each were fed balanced diets (10.7 +/- 0.4% protein) containing raw beans (Phaseolus vulgaris, L.), cooked beans or casein (control) as the single protein source, ad libitum. The animals were killed after 4 days and collagen was extracted from the tail and calcaneal tendons. Food intake and weight gain of rats fed raw beans (22 g, 0 g) were considerably less than rats fed cooked beans (38 g, 9 g) and casein (44 g, 22 g). Collagen was quantitated on the basis of hydroxyproline and corresponded to 0.1, 0.2 and 0.2% rat body weight, with specific radioactivity of 1.2, 1.6 and 4.2-mu-Ci/g, for the rats fed raw beans, cooked beans and casein, respectively. The results indicate that rats fed either bean protein synthesized less collagen than those fed casein (P<0.05). Although the food intake and extractable collagen of rats fed cooked beans were similar to those of casein-fed rats, weight gain and collagen specific radioactivity were less.255499501