Female BALB/c mice were immunized with either dianthin32 or momochin, type 1 ribosome-inactivating proteins (RIPs) derived from Dianthus charyophyllus and Momordica cochinchinensis, respectively. Five anti-dianthin32 and 6 anti-momochin secreting hybridomas were obtained by somatic fusion of lymphocytes with myeloma cell line NS0. The monoclonal antibodies (MAbs) produced were highly specific, as demonstrated by cross-reactivity assays performed with taxonomically related and unrelated type 1 RIPs, and recognized different epitopes of the antigen. The affinity constant of anti-RIPs MAbs ranged between 10(8) M-1 and 10(10) M-1.