A simple procedure is described for the routine morphological examination of different types of colonies and clusters in agar cultures. The following cytochemical methods are used for the identification of cells: naphthol-ASD-chloroacetate esterase, naphthol-ASD-acetate esterase with and without addition of sodium fluoride, Biebrich scarlet and acid phosphatase. Based on their cytochemical staining properties neutrophils, eosinophils, monocytes and macrophages can be readily identified in their different stages of maturation and an assessment made of the cellular composition of colonies and clusters.