The use of hydroxyproline analyses to predict the nutritional value of the protein in different animal tissues.

I . The amounts of available cystine and tyrosine in the protein of different animal tissues showed a close correlation with the level of hydroxyproline, and may be estimated from hydroxyproline values by regression equations. 2. Estimates of ‘chemical score’ have been calculated from the content of hydroxyproline determined in a series of samples for which net protein utilization (NPIJ) for rats had also been determined. Chemical scores calculated as percentages of the total ‘essential+ semiessential’ amino acid content of each material correlated closely with NPU, whereas scores calculated as percentages of total amino acids did not. ‘ Methionine f cystine’ were calculated to be first limiting amino acids in every sample.