Inoculation of lymph node or spleen cells from diabetic guinea pigs producing precipitating anti-insulin antibodies produced signs of immunodiabetes in young guinea pigs with cyclophosphamide-suppressed immunological reactivity. Blood sugar increased on day 5 after the cell transfer and distinct B-cell degranulation in the islets of Langerhans was noted on day 7. No distinct insulitis occurred, but infiltrates rich in plasma cells were found in the exocrine pancreas and parapancreatic tissue. Similar infiltration and slight decrease of β-granules was observed in permanently normoglycemic recipients of normal lymphoid cells. In control animals treated with cyclophosphamide only no such a reaction occurred.