The study has been performed to compare the ability of mouse peritoneal macrophages to ingest various types (catalase positive and negative) of bacteria and compared the influence of various sera on intracellular killing of Escherichia coli C (E. coli C). Among the tested microbes only E. coli C was ingested very luxuriantly and other organisms were taken up luxuriantly and moderately by mouse peritoneal resident macrophages (RMQs). Broad difference of ingestion was found even within the same genus (i.e., E. coli B and E. coli C). Intracellular killing of E. coli C by RMQs also varied depending on the type of serum. The maximum intracellular killing was found in the presence of normal mouse serum, although the difference was not much. The study has revealed that bacterial ingestion and intracellular killing ability of RMQs varies depending on bacterial strains and sera respectively.