Eight cell lines established originally at the Queensland Institute of Medical Research from human malignant melanoma explants have been studied by means of cytogenetic techniques. All showed abnormalities characteristic for each individual line and consisting of marker chromosomes and of changes in ploidy due to the addition of extra copies of normal chromosomes. Repeat cultures of some lines after one or two years contained most of the markers which had characterized the original samples; additional chromosome abnormalities were also found. An analysis of the break points concerned in the production of markers showed preferential involvement of chromosomes 1 and 5, with a prevalence of centromeric breaks on No. 1. These findings add further weight to the evidence suggesting that changes in chromosome 1 may be of special significance in the pathogenesis of some solid tumours.