CH31 and CH33 are B cell lymphomas whose growth in vitro is inhibited by anti‐Ig reagents, including both polyclonal and monoclonal anti‐μ antibodies, and an anti‐idiotype antiserum. Antibodies against class I or class II major histocompatibility complex antigens do not affect the growth of these cells. Inhibition is dependent on surface Ig cross‐linking and does not require ligand binding to Fc receptors. Interestingly, the inhibition of growth by anti‐μ, is reversed in CH31 (but not CH33) by E. coli lipopolysaccharide. These lymphomas should provide excellent models to study the mechanisms of growth inhibition mediated by surface Ig cross‐linking and the pathways of its reversal.