The gene coding for α tubulin has been isolated by the polymerase chain reaction and sequenced from 2 isolates of Neospora caninum (Nc-Liverpool and Nc-SweB1)The nucleotide sequence data reported in this paper are available from the GenBank database under the accession numbers AF508031 (N. caninum) and AY169962 (H. heydorni).. The data show that the gene, as in Toxoplasma gondii, is single copy and contains 3 exons and 2 introns and is identical in sequence in the 2 isolates studied. Comparison of the predicted protein sequence shows it to be identical to the α tubulin protein encoded by the T. gondii gene. The majority of the nucleotide substitutions that have occurred during the evolution of the T. gondii and N. caninum genes from their common ancestor have occurred in the third codon position. A partial coding sequence for α tubulin was also obtained from Hammondia heydorni and compared to other α tubulin sequences from Apicomplexa. The results show the sequences of the T. gondii, N. caninum and H. heydorni α tubulin genes to be similar but not identical in sequence, thereby providing new evidence that N. caninum and H. heydorni are genetically distinct species.