A simple method of using compactin for effective screening of microbial strains with high hydroxylation activity at the 6 beta position of compactin was developed. Agar plates containing different carbon sources and 500 mu g compactin mL(-1) were used to screen the microorganisms that can convert compactin to pravastatin. About 100 compactin-resistant strains were isolated from the Basal agar containing 7% (w/v) mannitol as a carbon source, in which two bacteria, Pseudomocardia autotrophica BCRC 12444 and Streptomyces griseolus BCRC 13677, capable of converting compactin to pravastatin with the yield of 20 and 32% (w/w), respectively, were found. High-performance liquid chromatography using C-18 column and two sequential mobile phases, 30% and 50% (v/v) acetonitrile, was also established to simultaneously determine the concentration of compactin and pravastatin in the culture broth. As such, about 2% of target microorganisms could be obtained from the screening program.