The prognostic relevance of 4 different serum markers (deoxythymidine kinase = S-TK, lactic dehydrogenase = S-LDH, S-Haptoglobin and S-Orosomucoid) in relation to histopathology according to the Kiel classification, stage and presence or absence of initial symptoms were investigated in 168 consecutive cases of low-grade non-Hodgkin lymphomas (NHL). All serum markers, as well as the other three parameters, gave prognostic information. Univariate analysis yielded a high predictive value (p less than 0.0002) for both S-TK and S-LDH. The best information regarding the probability of survival was, however, obtained from the presence or absence of symptoms from lymphoma manifestations other than those caused by a strictly local tumor mass. Since S-TK and S-LDH correlated well with each other, only the better of them, S-TK, gave information additional to initial symptoms in a multivariate test.