The in vitro granulocyte colony formation (CFU-C) was examined in 19 untreated patients with advanced Hodgkin's disease and in 25 untreated patients with histiocytic, lymphocytic, and mixed lymphomas. The patients with Hodgkin's disease and diffuse histiocytic, lymphocytic, and mixed lymphomas produced decreased numbers of granulocyte colinies, whereas patients with nodular histiocytic, lymphocytic, and mixed histiocytic-lymphocytic lymphomas showed normal granulycote colony growth. The acute response of CFU-C to combination chemotherapy (MOPP) is described in two patients followed with sequential marrow cultures through their indiction chemotherapy. The long-term effect of MOPP chemotherapy was examined in five patients who had completed chemotherapy 1.5-6 yr priot to in vitro examination.