['To better define the nature of the transient neutropenia shortly following granulocyte-colony stimulating factor (G-CSF) administration.', 'To evaluate the disappearance of neutrophils, we investigated neutrophil trafficking. Ratios of neutrophil number to background cellularity for C57BL/6 LysM-EGFP knock-in mice and rhesus macaques were determined in the lung, liver, spleen, and kidney after G-CSF administration.', 'For the C57BL/6 LysM-EGFP knock-in mice, the enhanced green fluorescent protein expression (EGFP(+)) cells increased in the lung and spleen within 15 minutes of administering 50 μg/kg G-CSF subcutaneously, and continued to increase in the lung and spleen from 15 minutes to 30 minutes. At 240 minutes, the pulmonary infiltrate declined to a level comparable to the level at 15 minutes, while in the spleen EGFP(+) cells continued to increase. For rhesus macaques, CD18(+) cells also significantly increased in the lung 30 minutes after administration of 10 μg/kg G-CSF subcutaneously compared to the control level.'] Is transient neutropenia after granulocyte-colony stimulating factor administration associated with neutrophil accumulation in pulmonary vasculature?