1. Hypertryptophanaemia, hypertryptophanuria and to a lesser degree a generalized hyperaminoaciduria were observed in phenylketonuric patients receiving certain commercial low-phenylalanine diets containing DL-tryptophan.
2. The generalized hyperaminoaciduria was associated with the ingestion of acid hydro-lysates of protein, but not with the ingestion of enzymic hydrolysates or D-tryptophan.
3. Alanine recovered from the urine of these treated patients had a D-isomer content of approx. 50%. This amount of urinary D-alanine could be derived from the ingestion of an acid hydrolysate of protein in which the amino acids had racemized to the extent of 2–3%.