Late heterologous and autologous stages of serum nephritis together with glomerular cells in culture are studied biochemically, morphologically and immunohistochemically for the assessment of the role of mononuclear leucocyte mediator system. The heterologous stage of the nephrotoxic nephritis is associated with the increase of Interleukin-I and TxA2 production. Role of Interleukin-I in the autologous stage is less pronounced in spite of proliferative activity of cultured mesangial cells. The effect of suppressive factors prevails in the glomerulus.