Standardized burns on rats were treated with 14C-labeled collagen from guinea pig skin. Collagen fractions of different solubility were extracted from the wounds during healing and the incorporation rates were measured. In the neutral salt-soluble fraction, maximal specific activity was found on day 7 after application of the burns; 1,65% of the applied label was incoporated, and it was calculated that 11,8% of the total neutral salt-soluble collagen of the wounds originated from the applied exogenous collagen. In the citric acid soluble collagen, maximal specific activity was observed on day 9; 1,48% of the applied label was incorporated; 6,0% of total citric acid-soluble collagen of the wounds was derived from the exogenous collagen. In the insoluble collagen, no significant increase in radioactivity was observed before day 14 after burning. The results support the opinion that exogenous collagen is used for substitution in connection with endogenous collagen synthesis.