Studies were carried out both on the quantitative and qualitative composition of aminoacids in the proteins of m. longissimus dorsi from cattle of the "Bulgarian Brown" breed with the help of an automatic aminoanalyzer Hd 1200 E, made in Czechoslovakia. Hydroxyproline and triptophane were determined at different analytical speeds. It was established that in the proteins of the muscle investigated are contained the following aminoacids, expressed in g/16 g N: lysine--7.77; treonine--4.09, valine--5.12, methyonine--2.50, isoleucine--4.67, leucine--8.42, phenylalanine--4.34, triptophane--1.40, histidine--3.37, arginine--6.17, aspartic acid--7.92, serine--3.31, glutamine acid--13.30, proline--3.73, glycine--4.79, alanine--4.99, tirosine--3.84 and hydroxyproline--0.59. The quantity of the essential aminoacids in the proteins of the muscle investigated from cattle, except the value of methyonine and cystine (the method we implemented does not secure the determination of cystine), surpasses the norm for their contents in the proteins suggested by FAO/WHO.