Successful treatment of severe fetal hemolytic disease depends on rapid and accurate measurement of fetal hemoglobin or hematocrit. The HemoCue is a portable hemoglobinometer that rapidly measures hemoglobin concentration. To evaluate the potential role of this instrument in fetal transfusion therapy, we measured hemoglobin concentration with the HemoCue and compared it with Coulter counter determination of hemoglobin in 39 fetuses. The HemoCue accurately measured fetal hemoglobin concentration (y = -0.3986 + 1.0276x; r = 0.97, P less than .001). This instrument is valuable for use with intravascular fetal transfusions.