Cell suspensions were prepared from fresh and paraffin embedded samples of lymph nodes from nine patients with non-Hodgkin's lymphoma. DNA flow cytometry was performed on these samples and the results from fresh tissue compared with those from paraffin embedded material. Results were compared in terms of DNA index (as a measure of aneuploidy) and S phase fraction (as an indication of proliferative activity). Good agreement was found between the results from the samples prepared by the two methods. The quality of DNA flow cytometry from paraffin embedded material was comparable with or better than that from fresh samples.