Multiple variations of the basic lymphocytotoxicity test have been reported to increase test sensitivity. Although these modifications are used routinely in crossmatch tests, as required by federal regulation, there has been no methodical assessment of the relative sensitivities and specificities of these techniques with the exception of the well-studied antiglobulin method. We have performed such a comparison and found that these modifications do not, uniformly, increase test sensitivity. We also observed that the effect of a technique modification on test sensitivity as measured by overall lymphocytotoxic antibody titer does not reflect, necessarily, the effect on HLA-specific antibody. It is widely believed that the antiglobulin method is the most sensitive of the lymphocytotoxicity techniques. We observed that while the antiglobulin method increased overall test sensitivity dramatically, we achieved a comparable level of sensitivity by either substituting B cells for T cells or doubling both the serum and the complement incubation times. However, no other technique modification detected as many HLA antibody specificities as did the antiglobulin method. The data presented here provide useful guidelines for selecting techniques for HLA typing, antibody screening, and cross-matching.