B cells that carry the complement receptor (CR+) were separated from B cells 
that lack the complement receptor (CR-) by velocity sedimentation or by passage 
through C-coated Sephadex columns. The kinetics of responses to bacterial 
lipopolysaccharide (LPS) in both B cell subpopulations were determined in three 
assay procedures: 1) incorporation of radioactive thymidine into DNA; 2) 
incorporation of radioactive leucine into immunoglobulin; 3) enumeration of 
cells forming polyclonal antibody to the 2,4,6-trinitrophenyl hapten. Although 
both subpopulations of B cells responded to LPS, they differed in the time 
course. CR- B cells responded with a delay of approximately 24 hr as compared 
with the response of CR+ B cells. The implications to the ontogenetic status of 
CR+ and CR- B subpopulations are discussed.