Human satellite DNAs I, II and IV were transcribed to yield radioactive complementary RNAs (cRNAs). These cRNAs were hybridised to metaphase chromosomes of man, chimpanzee (Pan troglodytes), gorilla (Gorilla gorilla) and orang utan (Pongo pygmaeus). The results of this in situ hybridisation were analysed quantitatively and compared with accepted chromosome homologies based on Giemsa banding patterns. The cRNA to satellite II (cRNAII) did not hybridise to chimpanzee chromosomes, although its hybridisation to chromosomes of gorilla and orang utan yielded more autoradiograph grains than hybridisation to human chromosomes, and cRNAIV hybridised to many chromosomes of gorilla and chimpanzee but was almost entirely restricted to the Y chromosome in orang utan. Most sites of hybridisation were located on homologous chromosomes in all four species, but there were a number of sites which showed no correspondence between satellite DNA location and chromosome banding patterns, and others where a given chromosomal location hybridised with different cRNAs in each species. These results are in contrast to those found for many transcribed DNA sequences, where the same sequence is usually located at homologous chromosome sites in different species, and appear to cast doubt on many proposed models of satellite DNA function.