A new polymer antiseptic, Catapol, to be used in the control of microorganisms attacking stone materials, was developed at the Institute of high-molecular compounds of the USSR Academy of sciences. Results of tests to evaluate its effects on microscopic and mould fungi and algae are reported and discussed. It is shown that Catapol provides protection of stone from fungal attack and eliminates the growth of algae. The need for further research on possible applications is stressed. 5 bibliographic references.