A multiplex allele specific polymerase chain reaction (MAS-PCR) based on the Cryptosporidium parvum dihydrofolate reductase (dhfr) gene sequence differentiates genotype 1 ('Human') from 2 ('Cattle') in a 1-step reaction. The MAS-PCR was validated on a panel of 34 microscopically positive C. parvum faecal samples of human and animal origin in comparison with 2 published PCR-restriction fragment length polymorphism (RFLP) methods targeting dhfr and the oocyst wall protein (cowp) genes. A validation panel of 37 negative faecal samples of human and animal origin was also tested in comparison with the cowp PCR-RFLP. MAS-PCR was found to be as sensitive for species detection as the most sensitive of the other tests, and detected more mixed genotype infections than the two other tests combined. In addition the MAS-PCR showed equivalent detection sensitivity in comparison with a published nested RFLP targeting the SSU rRNA gene, on a panel of prepared mixed genotype samples. The 1-step reaction is simpler and less expensive to perform than the RFLP methods, while the C. parvum specific amplicons and those for genotypes 1 and 2 (575, 357 and 190 bp respectively) can be easily distinguished on agarose gel.