The DNA fingerprinting method was used to resolve a canine paternity dispute. During the same estrus, a Shih Tzu bitch was inseminated by 2 dogs--a Shih Tzu and a Coton de Tulear. Because both breeds are alike phenotypically, it was difficult to decide whether the pups were purebred or of mixed breeding. The DNA bar codes indicated unambiguously that the 2 sires had fathered one pup each, thus documenting superfecundation.