The third and final meeting of a coordinated research programme on the diagnosis and management of thyroid disorders was held in Vienna from 15 to 17 December 1986. The participants were from Czechoslovakia, Egypt, Israel, Malaysia and Thailand. Each participant had studied between 500 and 1000 patients for thyroid function evaluation by performing T3, T4 and TSH radioimmunoassays. Each had also used the newly available supersensitive immunoradiometric (IRMA) assay in a group of patients to compare the efficiency of the new assay with that of the conventional assay. A microcomputer was provided to each participant for data analysis. Internal quality control was studied by establishing precision profiles and external quality control was on the basis of pooled standard sera in different ranges. Recommendation for the strategy suggested T4 RIA as the test of first choice in each category of thyroid function. IRMA TSH was suggested as a second test in borderline cases.