The procedures involving the growth of cell colonies in semi-solid media, such as methyl cellulose or agar, provide a score of colony-forming-units (CFUs) by means of morphology, and allow the application of cytochemistry. However, a better characterization of the growing cells by employing monoclonal antibodies is impaired by the medium itself. Plasma clot is a possible alternative, allowing immunofluorescence as well as immunoenzymatic techniques. We have developed a staining procedure which can be performed using both peroxidase- or alkaline phosphatase-conjugated reagents; the colonies, growing in plasma clot, can be stained in situ, without transferring the cells. In this paper we report on the study of six different cell lines stained by immunocytochemical techniques with appropriate monoclonal antibodies.