All possible crosses were made between European wild pigs with either 36 or 37 chromosomes and domestic swine with 38. The 36×36 cross produced only pigs with 36; the 36×37 and 37×38 crosses yielded the parent numbers in about equal numbers of pigs. All pigs resulting from the 36×38 cross had 37, while crossing 37×37 gave progeny with 36, 37 or 38 in about a 1:2:1 ratio. It is surmised that the three unpaired members in the 37-chromosome animal act as a trivalent during meiosis with two telocentric chromosomes behaving as a unit. No firm evidence indicated reduced fertility in any of the animals nor were any physical changes evident which could be associated with different chromosome forms.