A rabbit model was used to study the effects of neutropenia and inflammation on the intravascular distribution, survival, and tissue accumulation of transfused neutrophils. Donor blood labeled with [³H]thymidine was infused into normal or neutropenic (vinblastine treated) animals. Inflammation was created by subcutaneous implantation of polyvinyl sponges, some with added endotoxin. Initial circulating neutrophil pool recovery, survival, and inflammatory site accumulation of labeled neutrophils were measured.Neutropenia was associated with a relative increase in the marginal pool size, manifested by a diminished initial circulating pool (CNP) recovery of transfused cells. The CNP recovery was directly proportional to recipient neutrophil count. Neutropenia had no effect on the intravascular survival of transfused cells and was accompanied by only a modest decrease in the inflammatory site recovery of the transfused neutrophils (10.4±5.4 vs. 14.4±4.0% in normals).Inflammation in the form of subcutaneous polyvinyl sponges was accompanied by an increase in margination with initial CNP recoveries of 24.3±4.7 and 27.6±8.8% at zero and 4 h after implantation respectively (normal, 38.2±9.9%). Transit through the CNP was hastened by inflammation with a t_½ of 2.02±0.72 h (normal, 3.2±1.0 h).Addition of endotoxin to the sponges further perturbed cell kinetics. CNP recoveries were considerably lower and half-lifes were initially shorter and subsequently uninterpretable in studies done after endotoxin sponge insertion. Inflammatory site accumulation was markedly diminished to 7.4±1.9% of injected neutrophil label in the endotoxin sponge animals, suggesting that many of the transfused cells were functionally unavailable rather than marginated. These studies demonstrate that neutropenia and inflammation with or without endotoxin markedly alter the kinetics of transfused neutrophils and that CNP recovery of transfused cells is not necessarily predictive of their inflammatory site accumulation.