Twenty-one primary and 18 secondary monoclonal antibodies (mAb) with specificity for hen egg white lysozyme (HEL) were tested in pair-wise combinations for connectivity, that is, reactivity with each other in the absence of HEL, by an ELISA assay. All mAb reacted with at least one other, and a large proportion of the mAb, 7 of 16 primary and 11 of 18 secondary mAb, were reactive with 5 or more of the other mAb. Moreover, each gave a unique pattern of reactivity. Reactivity between mAb derived from primary and secondary hybridomas was also extensive. Some 'highly connective' mAb reacted with almost every other mAb tested. Two 'mini-networks' in the primary and secondary mAb, respectively, were identified through an ELISA binding assay and an inhibition study. Within these mini-networks (nets), members that bear IdC1 do not react with each other but bind to other members bearing IdC2. This type of interaction, as well as that between different nets defines a complicated network. No obvious correlation with fine specificity, presence of IdXE (a regulatory idiotype in the primary anti-HEL response), nor variable gene coding was apparent. Exact repeats of sequence were found for two pairs of mAb from independently selected hybridomas, i.e. in each case a primary and secondary hybridoma, indicating that high connectivity is associated with strong selection during B cell maturation following antigen stimulation.