693 kinds of indigenous plants randomly selected were screened for their antimicrobial activities against 23 different test organisms (Gram-positive, Gram-negative bacteria, yeast and fungi). The results of the testing showed that 250 (36%) kinds of the plants belonging to 72 families exhibited some level of antimicrobial action in vitro. Moreover, a microbiological prescreening program was employed in search of presumed cancerostatic plant products in crude extracts. These microbial tests based on agar diffusion techniques consist of prophage induction test and BIP test (bacteria inhibition-induction-phage inhibition). All active components selected by these microbial models are potential inhibitors of nucleic acid metabolism. A wide variety of plants was demonstrated to exhibit interesting activities in these screening systems. The bioactivity is uniformly distributed in various order. The screening results are briefly discussed.