We have developed a rapid and highly sensitive nonradioactive method for the detection of a mutant codon 12 human c-K-ras allele in the presence of as many as 10(4) copies of the wild type codon 12 allele. This sensitivity is achieved by selective polymerase chain reaction (PCR) amplification of mutant K-ras gene sequences employing a two stage procedure. The first stage entails the amplification of both K-ras mutant and wild type codon 12 sequences, followed by a selective restriction enzyme digestion of only wild type sequences. The second stage involves a subsequent amplification of undigested amplified fragments, enriched in mutant codon 12 sequences. These products are subject to restriction length polymorphism analysis for the detection of point mutations at codon 12. This technique is rapid, nonradioactive, and eliminates the need for either oligonucleotide hybridization or DNA sequencing. Variations of this selective amplification procedure may prove promising for the detection of specific point mutations in heterogenous cell populations.