Many practitioners believe in the phenomenon of being labeled either a “black cloud” or “white cloud” while on-call. A “white-cloud” physician is usually defined as one who sees fewer cases while a “black-cloud” is one who often receives more cases. To evaluate these phenomena, a 35-month prospective study was designed to evaluate the number of times apheresis staff was involved with emergent apheresis procedures at a large institution in the off hours between 10 pm and 7 am, since this is the time period when significant resources have to be mobilized to perform the procedure. During the study period, 92 emergent procedures (or “black-cloud” events, 8.6%) occurred. The median time between two consecutive “black-cloud” events was 9 days (range: 1–45 days). We found that there is no statistically significant association between the occurrence of “black-cloud” events and attending physicians (P =.99), nurses who had 56 or more days on-call during the course of the study (P =.28), year (P =.85), day of the week (P =.099), month (P =.57), or season of the year (P =.47). Therefore, the findings from this prospective 35-month confirmation study did not support the common perception that physicians or nurses maybe either “black clouds” or “white clouds.” It is important that this meaningful result be shared with apheresis practitioners given that the label of being a “black cloud” may have undesirable psychological implications to the physicians and nurses.