DNA:DNA colony hybridization techniques were used to select isolates from freshwater sediment samples that contain genes homologous to plasmid pSS50, coding for 4-chlorobiphenyl biodegradation. A high degree of resolution was achieved in which target organisms representing 0.3% of the total population were discerned. Initially, eight positive cultures were obtained, these were found to exist as consortia populations. Pure cultures, from the consortia, were then isolated and screened for 4-chlorobiphenyl degradative genes by DNA:DNA colony hybridization. Each strain demonstrating positive hybridization was subsequently shown to biodegrade 4-chlorobiphenyl to 4-chlorobenzoate. Following phenotypic characterization of the pure cultures it was found that three different organisms were repeatedly isolated from the various consortia populations. Field sampling to isolation of positive strains was accomplished within one week and completely avoided primary enrichment cultivation. (Copyright (c) 1986 Elsevier Science Publishers B.V. (Biomedical Division).)