Microorganisms containing short-chain-length (scl-) or medium-chain-length (mcl-) poly(hydroxyalkanoates) (PHAs) are commonly screened by applying rapid staining methods using lipophilic reagents. These methods provide powerful means for general screening of organisms actively producing and accumulating PHAs. The Southern blot hybridization method additionally allows the identification of potential PHA-producing microorganisms. Polymerase chain reaction (PCR)-based detection methods further afford rapid and sensitive means to screen for PHA biosynthesis genes. Specific PCR assays had been developed for the simultaneous or individual detection of the class 11 mcl-PHA synthase genes of Pseudomonas. The amplicons (similar to 0.54 kb) can be directly sequenced or used as probes for hybridization studies. The sequence information can further be used to initiate chromosome walking for an eventual cloning of the complete PHA biosynthesis operon. In addition, the amplification pattern and sequence data can be used to differentiate subgroups of organisms, as demonstrated for P. corrugata and P. mediterranea. Other researchers reported PCR methods for the detection of scl-PHA synthase genes and those of Bacillus spp., thus greatly expanding the types of PHA synthase gene and the organisms that can be characterized by this approach. The vast sequence information obtainable through PCR-based studies of various PHA synthase operons should facilitate the identification or construction of new PHA synthases capable of synthesizing novel PHAs.