A new technique measuring serum antoantibodies to lens proteins, employing antigen linked to magnetisable cellulose particles and fluorescent end-point detection, was used to examine patients with senile cataract and inflammatory eye disease. 40% of patients with senile cataract had antibodies to lens proteins, as did 28% of patients with heterochromic cyclitis and 20% of patients with uveitis, while there were no positive sera from patients with scleritis. The single patient with lens-induced uveitis had a high titre, but so did some patients with senile cataract. With the incorporation of a standard curve this technique offers a reliable quantitative assay for lens autoantibodies. It may provide a valuable tool for the investigation of pathogenetic mechanisms in cataract and inflammatory eye disease.