The immunoglobulin lambda light chain system displays a limited diversity in inbred mice. Indeed, the lambda locus is organized in two recombination units: V lambda 2-V lambda x-J lambda 2-C lambda 2-psi J lambda 4-psi C lambda 4, which can produce either lambda 2(V2) or lambda 2(Vx) chains; and V lambda 1-J lambda 3-C lambda 3-J lambda 1-C lambda 1, which can produce either lambda 1 or lambda 3 chains. Each of these units is associated with an enhancer, E lambda 2-4 or E lambda 1-3, at the 3' side. The expression of each lambda chain is, therefore, controlled by distinct promoter and/or enhancer regions. To clarify the basis of these controls, we measured, by quantitative polymerase chain reaction, the proportions of each lambda subtype in BALB/c spleen mRNA and among genomic rearrangements. It appears that these distributions are similar to and consistent with the relative cellular frequencies in the spleen, as evaluated by flow cytometry. These results suggest that, in resting cells, the transcription rates are identical, regardless of the lambda subtype. After lipopolysaccharide (LPS) stimulation, the transcription rates per cell remain similar for all lambda subtypes despite different regulatory sequences. To detect eventual post-transcriptional regulations, we estimated the lambda light chain distribution in IgM secreted by LPS-stimulated B cells and in serum IgG. These distributions are still similar to those of lambda-expressing cells, lambda mRNA or genomic rearrangements. We conclude that the lambda subtype distribution is conserved from productive V-J rearranged genes to secreted lambda immunoglobulins, despite different regulatory sequences.