We have compared the effects of the synthetic chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine (f-Met-Leu-Phe), on the deformability and chemotaxis of human polymorphonuclear leukocytes (PMNs). By utilizing the technique of cell elastimetry (deformability), which measures the negative pressure required to aspirate cells into a micropipet, we have shown a correlation between f-Met-Leu-Phe concentrations and PMN deformability which parallels the effects of that chemoattractant on filter chemotaxis. At concentrations as low as 10(-11) M, a change in the deformability characteristics of a population of neutrophils was demonstrated. The increase in deformability became most marked at peptide concentrations in the range of 1-5 x 10(-9) M, corresponding to the optimal concentration range in the filter chemotaxis assay. Concentrations of 10(-8) M and greater were associated with a significant increase in the negative pressure required to aspirate the cells into a micropipet. Alterations in PMN deformability, therefore, occur as a natural consequence of stimulation of a human PMN with a chemotactic factor and may be a prerequisite to efficient movement.