The amino acid composition, the electrolyte content, the titratable acidity, the osmolality and the pH of nine crystalline amino acid mixtures and one protein hydrolysate was analyzed and the results were compared with the data provided by the manufacturer. The amino acid composition of the protein hydrolysate (Aminosol 10 %) showed a marked discrepancy between the concentration of amino acids measured and the concentration given by the manufacturer. The sodium, chloride and especially the ammonia content is high as compared to the synthetic amino acid solutions. The amino acid composition of the crystalline amino acid solutions was generally in reasonable good agreement with the composition given by the manufacturers. In DL-Trophysan an unknown amino acid, probably alloisoleucine, was found. Only in two (Vamin 7 % and Amino acid solution 4200) out of eleven crystalline amino acid mixtures cystine and tyrosine could be detected; therefore only Amino acid solution 4200 and Vamin 7 % might be suited for infants. However, infants fed parenterally with Vamin 7 % often showed elevated levels of several amino acids. Amino acid solution 4200 with a composition similar to human milk seems to be more adapted and needs further investigation.