The haemolytic activity of the classical and alternative pathways, of factors B and D, as well as of the levels of C1q, C3 and C4 was determined in the serum of 24 adult patients with Hodgkin disease at different clinical stages. A marked reduction (p<0.001) of the classical and alternative pathways, of factor B and of the concentration of C3 and C4 was detected in the most advanced stages of the disease, IIIB and IVB. The data obtained in our paper suggest a possible association between the alterations of the complement system and the extension of the disease