Guinea pig polymorphonuclear leukocytes (PMNs), rich in glycogen granules, were collected from sodium-caseinate-induced eritoneal exudate. When these cells were incubated with rickettsiae, many microogranisms were phagocytized within 30 minutes at 35o C and vacuoles up to 5 μm in diameter containing glycogen granules were present. Contained within these vaculoes were phagocytized extracellular material and a dense, lysosomelike substance that was acid phosphatase positive. These vacuoles, which were interpreted to be autophagosomes, were absent from PMNs that had not been stimulated with microorganisms. The number of rickettsiae in the PMN did not appear to be related to the number of autophagosomes. About 8% and 80% of thin-sectioned profiles of PMNs contained these vacuoles after 30 minutes and 4 hours incubation, respectively. After 4 hours, the PMNs contained multiple autophagosomes. Almost all of the glycogen granules were in autophagosomes in some of the cells. In some PMNs, discontinuous membranes encirlced some glycogen. When PMNs were initally incubated with thorium dioxide and ferritin, and extensively washed prior to incubation with rickettsiae, glycogen was found surrounded by flattened secondary lysosmes containing the dense tracers. Some autophagosomes also contained the electron-dense tracers. These results suggest that rickettisae induce the rapid formation of glycogen-containing autophagosomes in guinea pig peritoneal PMNs in vitro.