Type 2 collagen is quantitatively the most important constituent of articular cartilage which is the target of progressive destruction in RA. Polymorphism of type 2 collagen could theoretically influence the development of RA either by rendering the cartilage matrix particularly susceptible to autoimmune attack or subsequent degradation. We have investigated the possibility that there is a common allele of type 2 collagen associated with RA by analysing a dimorphism of the corresponding structural gene (COL2A1) in healthy and diseased individuals. We compared haplotype frequencies, defined by the presence or absence of a Hind III restriction site at the COL2A1 locus (encoding type 2 collagen), in 98 patients with classical/definite RA and 158 controls. No differences were seen between the frequencies of individual genotypes in the two groups (maximum chi 2 = 0.7), indicating that susceptibility to this disease does not appear to be determined by the presence of a single common allelic variant at this locus.