The fourth ISBT/ICSH platelet serology workshop took place in 1988. It consisted of a wet workshop carried out by the 17 participating laboratories during March 1988, followed by a discussion of the results at a meeting of the ISBT/ICSH Expert Panel on Platelet Serology at the ISBT/BBTS Congress in London in July 1988. Sixteen samples,including 1 negative control serum, were analysed by the participants using methods of their choice. There was general agreement on 10/16 samples. The results indicated progress in the following areas: (i) antibody identification; (ii) differentiation of platelet-specific and HLA antibodies; (iii) glycoprotein localisation of platelet specific antigens; (iv) identification of new platelet antigen systems.