Abstract: A cyto(histo)chemical technique for determining inosine 5'-monophosphate dehydrogenase (IMPD) presence and concentration within one or more morphologically classified or classifiable cells taken from an animal or a human subject. Cell monolayers are prepared, fixed and stained according to a specified procedure in which inosine 5'-monophosphate (as enzyme substrate), nicotinamide adenine dinucleotide (NAD), phenazine methosulfate (PMS) and nitro blue tetrazolium (NBT) as a diazonium salt together produce a granular, dark blue deposit of formazan generally proportional to the IMPD activity in the cell. Cells are evaluated either visually or by image analysis, with a computerized image analyzer or other imaging system, according to accepted biostatistical methods and standards.