Purins or liquid fermented extracts of chipaca (Bidens pilosa L.) were prepared to establish the inhibitory effect of the actinomycetes found in such biopharmaceutical preparations on the growth of Phytophthora infestans (Mont) de Bary, the causative of potato late blight disease. Four purins made from flowers, roots, leaf-steams and a mixture of them were prepared; 25 actinomycete isolates were obtained from these purins and their ability to resist challenge by P. infestans was ascertained in medium plates using the ring Gauze technique and establishing initial concentrations of spores by microscopic counting in Neubauer chamber. Actinomycetes did not grow in flower purin as rhizosphere soil was not used in its preparation or because this particular pH (9) was higher than the normal range of 6 to 8 pH. Oomycete growth was inhibed in 8 actinomycete isolates (33.3% - 77.8% inhibition) from roots, stem-leaves and plant part purin mixtures. The greatest inhibition was obtained from isolates AC001, AC010, AC011 and AC025 (0.4, 6.0, 3.0 and 3.6 x 105 spore mL-1 count).