Porcine sperm chromosome karyotypes were obtained from two boars following heterologous in vitro fertilization (IVF) of zona-free hamster ova with ionophore-capacitated porcine spermatozoa. The karyotype yield per inseminated ovum was 9.3% (n = 1658), and there was no significant deviation from the expected 1:1 sex ratio (p greater than 0.5). Cytogenetic analysis revealed hyperhaploid (2.5%) and hypohaploid spermatozoa (1.9%). Spermatozoa with structural chromosome aberrations constituted 7.1% of the analyzed karyotypes, and these were predominantly chromosomal breaks, although acentric fragments were also found (2.6%).