Variations in the pH of the surrounding medium of hemocytes in vitro influence the morphology of granular hemocytes, the most predominant cell type in the hemocyte population of Emerita asiatica. Qualitative studies reveal that in the acidic range these cells become spindle-shaped and pseudopodial. Between pH 7.0 and 9.0 of the Tris-HCl buffer system, the hemocytes show a sequential change. The morphological features of the stages are facsimiles of the major hemocyte types occurring in the hemolymph of Emerita asiatica. The granular hemocytes become plasmatocyte- and cystocyte-like cells.Differential counts of hemocytes and pH-induced variations of granular hemocytes reveal that the rate of change decreases with decreasing pH of the surrounding medium. The aggregation of hemocytes increases with increase in pH.The pH-dependent variations of hemocytes indicate that for a truly objective definition of hemocyte morphology and for a strict classification into distinctly separate cell types, experimental analyses of hemocyte morphology are required.