1. The molecular weight of delta-globulin was estimated chromatographically to be about 10,700 daltons. 2. Ultracentrifuge experiments at 2-7 times 10-5 g gave values of s20, w = (1-49+0-16c) times 10- minus 13 s for the sedimentation coefficient and D20, w = (1-12+0-19c) times 10- minus 6 cm-2 s- minus 1 for the diffusion coefficient, c being the protain concentration (g/100 ml). 3. According to the Svedberg equation, these imply a molecular weight of 12,470 daltons, assuming v = 0-74 ml/g. 4. Using refractometer measurements of protein concentration it was found that E-1% 1cm (278 nm) = 5-57 at pH 7-8. 5. From the ultraviolet absorption spectrum of the protein in 0-1 N NaOH it was concluded that the molecule probably contains four tyrosine residues and no tryptophan. 6. On this basis a revised amino acid composition is given.