An anticardiolipin wet workshop was conducted at the Fifth International Antiphospholipid Symposium (San Antonio, Texas, September 9-12, 1992). The workshop had four objectives: 1. to determine variability in measurement of immunoglobulin (Ig) G, IgM, and IgA anticardiolipin of eight unknown sera; 2. to examine the correlation between three commercial enzyme-linked immunosorbent assay (ELISA) kits and the Antiphospholipid Standardization Laboratory; 3. to examine protocols by which anticardiolipin binding to phospholipid antigens and beta 2 glycoprotein 1 (beta 2GP1) might be compared; and 4. to examine the beta 2GP1 effect on cardiolipin binding activity. Results showed good overall correlation of quantitative anticardiolipin measurements between workshop participants and the Antiphospholipid Standardization Laboratory. Correlation with individual ELISA kits was also good. With respect to the third objective, all participants showed comparable binding to cardiolipin and phosphatidylserine but none to phosphatidylcholine or beta 2GP1. Finally, beta 2GP1 enhanced, but was not essential for, anticardiolipin binding. This workshop will not settle controversies about anticardiolipin measurement and specificity, but suggests protocols to resolve these issues.