We analyzed protein expression of cyclin D1, cyclin D2, and cyclin D3 using high-resolution enzymatic amplification staining and flow cytometry in the neoplastic cells from 80 patients with CD5+ B-cell lymphoproliferative disorders. The D cyclins were expressed differentially in chronic lymphocytic leukemia (CLL), prolymphocytic leukemia (PLL), and mantle cell lymphoma (MCL) with strong staining of cyclin D1 and D2 in MCL, strong staining of cyclin D1 but weak staining of cyclin D2 in 4 of 5 PLLs, and low-level staining for both cyclins in most CLLs. No correlation between cyclin D1 and D2 and growth rates or CD38 expression was observed. However, cyclin D1 levels were significantly higher in ZAP-70+ CLL cases, although no association between ZAP-70 and cyclin D2 was detected. The results indicate that flow cytometric analysis of D cyclins may help in classification of CD5+ B-cell lymphoproliferative disorders.