A novel approach to screen hybridomas producing antibodies directed against ricin was developed. Anti-ricin antibodies were produced and characterized based on protection of Sp2/mIL6 myeloma cells and in vivo studies demonstrating neutralization of the toxic effects of ricin in mice. During the production of hybridomas, cells were plated in media supplemented with hypoxanthine, aminopterin, and thymidine supplement (HAT), HAT + ricin, or ricin. Three hybridomas, designated HRF4, HHRD7 and HHRD9, were selected from the media supplemented with ricin and were shown to produce antibodies directed against ricin. Intraperitoneal injection of hybridoma supernatant containing anti-ricin antibodies combined with 0.5 microg ricin (a toxic dosage) protected Balb/C mice from the deleterious effects of the ricin. Hybridoma, HHRD9, did not contain high titre antibodies to ricin but appeared to neutralize the toxic effects of ricin in mice.