A highly sensitive quantitative fluorometric assay for phagocytosis, previously 
measured using fluorescence spectrophotometry or flow cytometry, has been 
adapted for use with a 96-well fluorescence plate reader. The technique allows 
rapid analysis of large numbers of samples, and requires only a small sample 
volume. Comparison of plate types demonstrated that opaque white 96-well 
luminostrips produced a 100 fold greater fluorescent output, and were more 
sensitive than black fluoroplates. Intraplate variability was also significantly 
lower using white luminostrips. For the phagocytic assay, fluorescein conjugated 
polystyrene beads were incubated with macrophage monolayers in white 
luminostrips. After incubation, cells were washed, lysed and phagocytosis 
quantified by determining the fluorescent intensity using a fluorescence plate 
reader. The number of beads phagocytized was determined from a standard curve of 
bead number versus fluorescent output. The phagocytic activity of resident and 
thioglycollate-elicited peritoneal macrophages was compared using this 
technique.