BACKGROUND The aim of the present was to determine the levels of the tumor necrosis factor (TNF)-alpha in patients with HIV infection to study the relationship with the concentration of triglycerides (TG), CD4 lymphocyte count and clinical diagnosis. METHODS Seventy-eight HIV-infected patients (58 males, 20 females); mean age 32 years presenting different clinical situations were studied. TNF, TG, CD4 lymphocyte count, and clinical diagnosis at the time of the study were analyzed. RESULTS The mean TNF values in the sample was 25.5 x 10(-3) pg/l with a confidence interval of 95% (Cl 95%), 16.6 x 10(-3) pg/l to 34.4 x 10(-3) pg/l with a trend to being higher in the group with less than 200 x 10(6) CD4/l (Cl 95%: 18.6 x 10(-3) pg/l-44.3 x 10(-3) pg/l). Mean TG values in the sample were 2.02 milligrams (Cl 95%: 1.72 milligrams-2.31 milligrams) being significantly higher in the group with less than 200 x 10(6) CD4/l (X = 2.35 +/- 1.32 milligrams; p < 0.005). TNF concentrations were found to be significantly higher in the group with acute infection (Cl 95%: 27 x 10(-3) pg/l-69 x 10(-3) pg/l) with respect to the group without infection at the time of the study (Cl 95% 7 x 10(-3) pg/l-19 x 10(-3) pg/l). The correlation coefficient between TNF and TG was r = 0.34 (p = 0.01). CONCLUSIONS Both the tumor necrosis factor and triglycerides are high in patients with HIV infection and CD4 lower than 200 x 10(6)/l. The correlation between tumor necrosis factor and triglyceride concentrations is positive and significant. The increase in the former is more important when there is concomitant infection and could be considered as a marker of opportunistic infection.