A monoclonal antibody to proliferating cell nuclear antigen (PCNA/cyclin) has recently become available. This antibody, as opposed to Ki-67, can be used on formalin-fixed, paraffin embedded tissue sections and allows retrospective comparison of PCNA positivity to percent S + G2 + M of the cell cycle. To compare fresh lymphoma deoxyribonucleic acid (DNA) analysis with PCNA activity on fixed, paraffin-embedded sections, prospective flow cytometric studies of cell cycle analysis were performed on lymph nodes removed from 10 patients for diagnosis. Six patients had T-cell lymphoma, two had B-cell lymphoma, and two were benign. Using the peroxidase-antiperoxidase method, the nuclear positivity of archival lymphoma cases was also examined. To quantify PCNA positivity, a unique morphometric method was employed that utilized digital imaging by high definition television and ELAS (Earth Land Application Software), a geoscience software used extensively for color quantitation of remote sensed data. The immunologic percent PCNA positivity was 26.1 +/- 20 vs. percent S + G2 + M by flow cytometry of 22.4 +/- 10 with a correlation coefficient (r) of 0.55. This r-value compared favorably to data generated for Ki-67 in solid malignant neoplasms. The six more concordant cases had a percent PCNA positivity of 26.5 +/- 10.0 and a percent S + G2 + M of 27.3 +/- 8.6, r = 0.96. Our study is unique in that it compared fresh lymphoma DNA analysis data with paraffin PCNA data. It is our conclusion that immunologic PCNA positivity in paraffin sections correlates with fresh flow cytometric S + G2 + M in lymph nodes, although careful attention must be paid to the area of the node quantified for PCNA.