We describe a laboratory exercise in DNA profiling that can be used in an undergraduate biochemistry teaching laboratory to demonstrate four fundamental procedures: isolation of genomic DNA from human (cheek) cells, use of the polymerase chain reaction (PCR) to amplify DNA, separation of amplified DNAs on agarose and polyacrylamide gels, and quantitative analysis of data (while comparing two different gel separation techniques). The target of PCR amplification is the 369–801 base pair D1S80 locus of the human genome, a variable number of tandem repeats (VNTR) locus containing a 16 base pair repeat unit. Students amplify DNA from their entire class, determine the size and genotype of all of the students' D1S80 loci by two gel separation techniques, compare the samples to an "evidence" sample to solve a fictitious crime, and critically evaluate the methodology.