The effect of feeding rats a low-protein diet (1%) and its duration (4, 8, 12 and 16 weeks) on the protein content and the amino acids pattern of hair were studied. These variations were compared with control group fed an adequate protein diet (16%). Protein content of hair was diminished in the protein deficient rats after four weeks followed by a gradual decrease till the end of the experiment. Sulphur-containing amino acids cystine and cysteine were significantly reduced in the hair of the protein deficient rats when compared with the controls. The amino acids patterns showed significant differences from controls by the end of the whole experimental period.