Cytochemical reactions were examined in lymph node imprints from a group of 53 previously untreated patients with histologically proven Hodgkin's disease. In 40 of 51 cases investigated, Reed-Sternberg (R-S) cells, irrespective of the cytologic appearances and the histologic types, showed moderate to strong reactions with acid phosphatase (ACP). In 12 cases ACP activity was present in more than 25% of the R-S cells. The reaction consisted of formation of small- to medium-sized granules, which were located close to the nuclei on a diffusely positive background or irregularly distributed throughout the cytoplasm. In three cases, a coarse granular reaction product with periodic acid-Schiff was present. R-S cells were positive to the naphthol-AS acetate esterase and beta-glucuronidase reactions in four and two cases, respectively. Alkaline phosphatase and naphthol-AS-D-chloroacetate esterase reactions were completely negative. Our results have revealed a pattern of staining in the diagnostic R-S cells similar to that in its morphologic variants; this supports the view that these cells may derive from a common primitive cell. Moreover, the quality and quantity of the ACP reaction product shows that R-S cells differ from both neoplastic histiocytes of malignant histiocytosis and neoplastic lymphocytes of T-cell lymphomas. This study confirms that R-S cells lack definite cytochemical characteristics of each of supposed progenitor cells: histiocytes and T-lymphocytes.