In rat bone marrow (BM), the B lineage surface antigen HIS24 is expressed by all surface mu chain-bearing (s mu+) B cells, by cytoplasmic mu chain-containing (c mu+s mu-) pre-B cells and TdT+ cells, and by lymphoid cells lacking both mu and TdT. Because TdT+ and HIS24+TdT-mu- cells may represent stages in B lymphocytopoiesis before mu chain expression, we investigated their kinetics. The metaphase arrest method was combined with immunofluorescence staining to detect proliferation and to quantitate cell production in the BM pre-B, TdT+, and HIS24+TdT-mu- compartments. Their apparent cell cycle times (tC(a)) were 38, 36, and 19 hr, and the number of cells produced per hour per femur were 58, 9, and 41 X 10(4), respectively. The HIS24+ compartments showed further phenotypic heterogeneity. Six percent of TdT+ cells expressed mu chains and were therefore pre-B cells. Twenty percent of HIS24+TdT-mu- cells expressed Ig other than mu chains, with size distribution and kinetics similar to HIS24+TdT-Ig- cells. Thus, the rate of production in the truly Ig-HIS24+ compartment was about 40 X 10(4)/hr/femur (8.5 by TdT+mu- and 33 by TdT-Ig-). In each phenotypic compartment, mitoses were confined to subsets of large (greater than 11 to 12 micron) cells with tC(a) of 13 to 15 hr. Surface mu+ B cells were essentially non-cycling. To quantitate whole body BM cell production, the recovery of marrow from bone and the distribution of BM were measured in 59Fe distribution experiments. The number of cells produced by whole body BM was estimated as follows: for pre-B cells, 4.5 X 10(8)/day; for TdT+mu-, 0.7 X 10(8)/day; and for HIS24+TdT-Ig- 2.6 X 10(8)/day. From the derived cell flux in these compartments we suggest that 1) many more pre-B cells are produced than needed by the peripheral B cell pool; 2) if TdT is an obligatory stage in B cell genesis, there must be at least two cell cycles in the pre-B cell compartment; 3) if it is not, the TdT+ stage may be bypassed, with HIS24+TdT-Ig- cells perhaps feeding directly into the pre-B cell compartment.