The polymerase chain reaction (PCR) technique has provided a substantial improvement for the detection and analysis of known genetic polymorphisms. Here, we describe the application of this method for the detection of variable number of tandem repeat (VNTR) sequences. With the use of unique oligonucleotide primers, flanking the repeat sequence, and the thermostable Taq DNA polymerase, the hypervariable regions 3' of the Ha-ras gene, 3' of the apolipoprotein B gene, and 5' to the joining segments of the heavy-chain immunoglobulin gene could be amplified. Alleles up to 2,000 bp could be visualized directly on ethidium bromide-stained agarose gels. Larger alleles were seen only after traditional Southern blot analysis with an internal probe. The value of this new approach for the detection of VNTRs is illustrated in a case of paternity dispute.