Clear correlations have not been established between bone marrow cellularity before or at marrow harvest and marrow cell yield for transplantation. The authors therefore retrospectively reviewed 204 marrow donations to ascertain whether biopsy cellularity was predictive of nucleated cell yield at harvest, as measured by final cell counts (FCC)/kg body weight. Preharvest and intraoperative biopsy cellularity were highly correlated with each other; moderate correlation was found between intraoperative biopsy cellularity and FCC. Mean cellularity was slightly but significantly higher in samples yielding an FCC greater than 2 x 10(8) nucleated cells/kg (P < 0.01). Biopsy cellularity less than 20%, seen in 4% of specimens, did not consistently correlate with low FCC, defined as less than 2 x 10(8) nucleated cells/kg. More than 2 x 10(8) cells/kg were consistently obtained only when biopsy cellularity was 65% or more. Marrow biopsies performed before harvest can be used to predict intraoperative cell counts at the time of marrow donation, although a cell yield of more than 2 x 10(8) nucleated cells/kg can be assured only with high marrow cellularity.