A project was conducted to clone the genes encoding the polypeptide subunits of the enzyme methyl-coenzyme M methyl-reductase (methyl CoM-reductase). The experimental approach was to purify the enzyme, produce antibodies against the enzyme, and use these antibodies to screen Escherichia coli colonies for clones that synthesized antigens with which the anti-methyl CoM-reductase antibodies reacted. The E. coli strains contained plasmids or were preinfected with bacteriophages that had been constructed by in vitro DNA recombinant techniques to contain fragments of either M. thermoautotrophicum or M. vannielii genomic DNA's. The expectation was that the E. coli clones that reacted with the anti-methyl CoM-reductase antibodies would contain cloned methanogen DNA sequences encoding part or all of the methyl CoM-reductase polypeptides. However, this technique frequently generated false positive signals. Most of the study period was used in improving the technology to decrease the number of antifactually positive signals and in screening and analyzing positive clones that ultimately were found to contain none of the desired genes.