We have developed and tested a rapid and sensitive method of detecting expansion of T-cell clones using the polymerase chain reaction (PCR) and a single set of consensus primers for the V and J regions to amplify rearranged T-cell receptor-gamma (TCR-gamma) genes. Monoclonality was continued in all of the 18 cases of T-cell neoplasms tested, but not in reactive lymphadenopathy, non-Hodgkin's B lymphomas, and Hodgkin's disease. PCR analysis, using the primer sequence outlined in this study, had an overall specificity of 100% when compared with Southern blot analysis. No false-negative results were observed, certainly owing to the choice of consensus primers and to the control of PCR reactions on agarose gels before testing for clonality by separation of PCR products on polyacrylamide gels. This method for the detection of T-cell monoclonality can be especially useful in cases that are diagnostically problematic with standard histological and immunological analysis and in cases where the material available is limited.