Small numbers of leukocytes cannot be counted by automated methods. So we performed fluorescent staining of leukocyte DNA and analyzed 50 samples of single-donor PC by FACS. In 72% of these PC we found white blood cells (WBC) < 5/microliter = WBC < 10(6)/U. Nevertheless we do filter our PC. Should fresh frozen plasma (FFP) be irradiated for immunocompromised patients to prevent TA-GvHD? To evaluate the number and distribution of WBC in FFP we stained WBC with moAb and performed FACS analyses. We found WBC 7.164 +/- 5.66 x 10(6)/U, lymphocytes, 3.032 +/- 3.66 x 10(6)/U and T lymphocytes 2.135 +/- 2.02 x 10(6)/U. According to these data it should be considered to irradiate FFP for immunocompromised patients.