The effect of the protein precipitants acetone, acetonitrile, perchloric acid and trichloroacetic acid on free amino acid concentrations in supernatants from ovine plasma and bovine serum albumin solutions was determined. The organic precipitants decreased (P < 0.05) free amino acid concentrations in a protein concentration dependent manner while the acid precipitants had no effect. Key words: Amino acids, protein precipitating agents