An increasing number of Holstein calf births exhibiting vertebral deformations has been detected in Denmark since 1999 by a program monitoring the incidence of genetic diseases. Pedigree analysis demonstrated that the affected calves originated from a family afflicted by an autosomally recessively inherited complex vertebral malformation (CVM) syndrome. To determine the actual carrier frequency of the CVM-determining mutation in a population of Polish Holstein-Friesian (=Polish Black-and-White) cattle, we examined 202 proven bulls (active in 2001-2005) used by 4 domestic artificial insemination companies and 403 unproven bulls (under evaluation for breeding value). Out of the 605 bulls examined, 150 T/G heterozygotes were diagnosed, including 118 that were sons of known CVM carriers. Identification of a gene polymorphism in a bovine solute carrier family 35 member 3, termed SLC35A3, was conducted with the use of a new PCR-SSCP method (polymerase chain reaction - single stranded conformation polymorphism), which - due to its ease of use and high reliability - can be applied in widespread screening programs aimed at reducing the incidence of the CVM defect.