This paper describes physiochemical and biological properties of 3 immunologically active compounds extracted by acetone from porcine skin. High pressure gel chromatography confirmed their heterogeneity. RP-HPLC of compound 2 (C2 or K-activin) also characterizes it as a heterogeneous entity. It was shown to inhibit proliferation of cultured fibroblasts from human fetuses and exhibit weak activity in general anaphylactic reaction (anaphylactic shock) and skin anaphylactic reaction. A summary of data on immunologically active compounds are presented with special emphasis laid on acetone-extractable K-activin.