Marrow specimens were obtained from 34 different individuals (mainly stage I or II Hodgkins or Lymphomas) and evaluated for their content of erythropoietic and granulopoietic progenitor cells using conventional colony assay procedures and a standardized set of re-agents. Frequency distributions showed that the data for all types of progenitors appeared to be log normally distributed. Estimates of compartment size (i.e. no. of progenitors per 2 X 10(5) buffy coat cells) were 107 CFU-E, 70 BFU-E (37 classified as mature, 12 classified as primitive) and 64 CFU-C. The ratio's of CFU-E: mature BFU-E: primitive BFU-E numbers in vivo correspond well to those predicted by their proliferative capacity in vitro. Interestingly the spread of values obtained for each erythropoietic compartment was not the same but decreased with progressive differentiation, suggesting that stringent regulation of red cell output may not occur until the latter stages of erythroid cell maturation. The ratio of total BFU-E: CFU-C numbers was 1.25 +/- 0.15 suggesting that on average the probability of stem cell commitment to either the erythropoietic or granulopoietic pathway may be roughly equal.