We developed a novel and convenient neutrophil adherence test for ascertaining the activated state of neutrophils. Human peripheral blood neutrophils were placed in wells of a 96-well flat-bottom culture plate, and incubated in the presence or absence of neutrophil stimulants for varying periods of time at 37 C in a CO2 incubator (5% CO2, 95% air). After non-adherent cells were completely removed by vibration on a vortex mixer, residual adherent cells were fixed and stained with crystal violet containing 12% formaldehyde and 10% ethanol. After thorough washing, 1% SDS was added to the plate, and the absorbance of each well was measured at 570 nm. Our results correlate well with those of a previously reported method using 51Cr-labeled cells.