Serologic tests do not reflect the functional activity of antibodies, hence cellular bioassays, namely the monocyte monolayer assay, the antibody-dependent cellular cytotoxicity assay, and the chemiluminescence test, have been introduced. Overall, they appeared to be helpful in the assessment of clinical importance of antibodies, although the initial expectations have not been met. These assays are most useful in patients who require blood transfusion(s) and who have an alloantibody without clear clinical significance, usually against a high frequency antigen. Such patients, if their monocyte monolayer assay result is negative, will not develop an immediate hemolytic reaction after transfusion of incompatible red cells. In predicting the severity of hemolytic disease of the newborn, cellular bioassays are less useful. They should be used only in conjunction with ultrasonography, consideration of the outcomes of previous pregnancies, and antibody quantitation. They are helpful in weighing the risks of invasive procedures in women with borderline levels of anti-D. There is, however, no convincing evidence that cellular bioassays reduce the number of unnecessary amniocenteses and cordocenteses. Chemiluminescence tests seem to be most useful, and antibody-dependent cellular cytotoxicity assays are almost as useful. Falsely positive results may be reduced by excluding that the fetus is Rh positive or by detecting the Fc gammaR-blocking antibodies in maternal serum.