Quantitative models describing the dynamics of human neutrophils in the microcirculation require accurate morphometric parameters such as volume and surface membrane area. Using both a micropipette technique and video light microscopy (LM) to measure the diameters of the spherical cells, we have accurately determined the volume of the human neutrophil. Our value, 299 +/- 32 microns 3, is in good agreement with our earlier results, but 55% larger than that reported by Schmid-Schönbein et al (Blood 56:866, 1980). However, the measurements of Schmid-Schönbein et al were based on the actual mass of the cells derived from transmission electron microscopic (TEM) images. The membrane surface area, at lysis, was calculated to be 2.6 times its initial projected area. After lysis, the cells do not reduce their size, indicative of the possibility of a F-actin network formation that would stiffen the structure. Further, we show that neutrophils behave as ideal osmometers when exposed to anisotonic solutions at 21 degrees C, as predicted by the Boyle-Van't Hoff relationship. The calculated Ponder's value, R, is 0.77, which corresponds to 77% of the cell volume being osmotically active under isotonic conditions. However, at 37 degrees C, the cells are able to regulate their volumes toward the original volumes after an osmotic stress.