Equilibrium dialysis, gel filtration and SDS polyacrylamide gel electrophoresis were used to study the interaction of sodium salt of 9-oxo-10-acridineacetic acid (CMA) as well as its analogs 7, 8, 11, 13 - 16 with proteins. The compounds were found to bind mainly to serum albumins. Several other proteins had no affinity to the compounds. The close analogs 7 and 8 (sodium salt of 2,7-dibromo-9-oxo-10-acridineacetic acid and sodium salt of 9-oxo-10-acridinebutyric acid) which were inactive as interferon inducers were found to have greater affinity to bovine, mouse or human albumin than the active IFN inducer--CMA. The mechanism of interaction of CMA as well as its close analogs with albumin resembled the first phase of reaction of pharmacologically active ligands with their specific receptor or acceptor proteins. CMA and some of its close analogs were also shown to stabilize the human erythrocyte membrane against hemolysis in the hypotonic solution. However, the activity of the compounds was much weaker than that of other so called membrane active drugs.