A modification of connective tissue air bleb technique was used to develop a model system in inbred strains of mice for the study of chemoattractants in vivo. The method was developed using the well characterized n-formylated chemotactic peptide, f-Met-Leu-Phe, as the positive control. Injection of 0.1 ml of f-Met-Leu-Phe solutions from 10(-7) to 10(-10) M resulted in an influx of polymorphonuclear leukocytes within 2 h. Study of the kinetics of the response showed that the number of infiltrating cells reached a peak within 8 h and slowly declined over a 2-day period. The predominant infiltrating cell type during the first 24 h was the polymorphonuclear leukocyte. Between 24 and 48 h the polymorphonuclear leukocytes were replaced by monocytes. By utilizing an inbred mouse strain (DBA-1J and 2J) sufficient or deficient in C5 it was possible to distinguish compounds that were directly chemotactic from those that worked indirectly, or whose chemotactic potential could be enhanced by generation of the chemotactic complement split product C5a. The method was found to be technically simple, reproducible and semi-quantitative and represents a good model system to facilitate the comparison of chemotactic responses in vivo and in vitro.