Laser flow cytometric analysis is well suited to many clinical immunofluorescent and hematologic applications. One of these is automated reticulocyte and platelet enumerations. We have performed a clinical evaluation of a fluorescence laser flow cytometer reticulocyte and platelet enumeration method using the fluorochrome acridine orange. One hundred and thirty-two clinical specimens from inpatients in our comprehensive cancer center were analyzed for platelet counts and 101 samples from the same population were analyzed for reticulocyte counts by the flow cytometer and simultaneously by conventional techniques. Both the reticulocyte and platelet enumerations achieved a high degree of correlation with standard methods for the nonbone marrow-transplant patients studied (R = .989 for reticulocytes and R = .995 for platelets). Marrow transplant patients had a slightly poorer correlation coefficient for the reticulocyte enumeration (R = .923), but analysis of serial determinations of these patients' samples for reticulocyte counts revealed that results were more consistent over time with the automated method than with the traditional manual method. The laser flow cytometer fluorescence reticulocyte and platelet enumeration methods described are efficient, rapid, and reliable for platelet and reticulocyte counting.