The chromosomes of the giant forest hog, Hylochoerus meinertzhageni, the warthog, Phacochoerus aethiopicus and the bush pig, Potamochoerus porcus an studied. Their sex-and nucleolar chromosomes are compared mutually and with those of the domestic pig, Sus scrofa. AU four species have similar X and Y chromosomes. The only bush pig sow examined, however, exhibits an extraordinary situation with two very different X chromosomes. One of these X's, which is of the ordinary type, is present in the boars together with a Y.

The chromosomes and the anatomy and histology of the reproductive tract of two intersexual pigs were investigated. The animals displayed mosaicism in the leucocyte population with an XX : XY ratio of 1 : 3 and 2 : 1, respectively. Anatomically the former animal most probably was a male hermaphrodite; the latter a true hermaphrodite. In non-hemopoietic tissue, i.e. fibroblasts from kidney, lung and spleen, all cells had a chromosome set with two X-chromosomes. The possibilities that the two investigated pig intersexes were freemartins are discussed.

The karyotype of the pig (Sus scrofa domestica) is studied and characterized after applying G‐band and C‐band staining procedures. The material examined originates from 5 boars and 5 gilts and consists of cells from fibroblast and lymphoblast cultures. The identity of the X‐chromosome is discussed.

Some procedures to obtain G‐bands and C‐bands in chromosomes are presented. They are demonstrated in porcine and rabbit cell material.

The chromosome conditions of a malformed and stillborn piglet are described. The animal was a chromosomal mosaic with two clones, one with the normal chromosome complement and one with a reciprocal translocation. The translocation had taken place between the longest chromosome and one of the smallest metacentric ones. The significance of the mosaicism for the malformation of the animal is discussed.