Three fractions with different molecular weights were isolated from pig skin. Fraction 1 (F1) and fraction 3 (F3) stimulated human keratinocyte proliferation in primary and regenerating cultures, but didn't affect their differentiation. Fraction 2 (F2) inhibited keratinocyte proliferation and stimulated their differentiation. The content of the proteins, carbohydrates, ribonucleic acids (RNA) and total lipids were determined in the fractions. The content of proteins and total lipids decreased from F1 to F3, but the content of carbohydrates and RNA increased. Physico-chemical properties of the fractions were studied by the methods of isoelectric focusing and vertical electrophoresis in polyacrilamide gel with sodium dodecyl sulphate and 7 M urea. The authors found that F1 contained 2-3 main proteins with molecular weight of 58 kDa and pI from 4.9 to 5.1 and RNA with molecular weight of 44 kDa. F2 was more heterogeneous. It contained a few main proteins with molecular weights from 6.9 to 61 kDa and pI from 4.4 to 8.3 and RNA with approximate molecular weights from 5.0 to 7.5 kDa. F3 contained a few main proteins with molecular weights from 3.5 to 59 kDa and pI from 4.8 to 5.1 and RNA with approximate molecular weights from 4.8 to 7.0 kDa.