This paper reports on three applications of the polymerase chain reaction (PCR) in the pathology laboratory, cystic fibrosis carrier status investigation, Staphylococcus aureus identification and HLA-DQ alpha tissue typing. Allele specific PCR was used to detect the common cystic fibrosis mutation (delta F508) in an Irish family. The genomic status of each member was shown to be either heterozygous (carrier) or homozygous (affected) for the mutation, based on the resolution of allelic amplifications in an agarose gel. Five staphylococci were subjected to PCR designed to amplify a 137 bp DNA fragment from the S. aureus protein A gene (spa). Four isolates gave a coloured "dot-blot" positive signal, the fifth was negative. In the final application the HLA-DQ alpha region was amplified using DNA obtained from four unrelated individuals. Amplified DNA was tissue typed in a reverse "dot-blot" format. All individuals had unique HLA-DQ alpha types. These examples have been chosen to demonstrate the versatility of this technique and to illustrate some of its potential applications.