Summary and Conclusions Studies with Staph, aureus, S. dysentetriae Sonne, and B. cereus indicate that streptomycin is adsorbed by bacterial cells, all or nearly all of the adsorption occurring at the cell surface. There was no demonstrable difference in adsorption between susceptible and resistant strains of these organisms. The affinity of streptomycin for bacterial cells is greatly reduced in the presence of NaCl. Evidence is presented indicating that the persistent action of streptomycin in vivo after the blood level falls below a detectable value is not related to a slow desorption of streptomycin from the adsorbed state on bacterial cells.