['Endomyocardial biopsy is the gold-standard procedure to diagnose acute cellular rejection after heart transplantation. This study assessed whether the blood levels of cytokines involved in inflammation and immune activation are useful to detect the presence of acute cellular rejection.', 'Blood specimens collected before 275 endomyocardial biopsies in 66 patients were assayed for levels of TNFalpha, IL6, IL1beta, and IL2 receptor. The biopsies were grouped according to the presence (n = 41) or absence (n = 234) of acute cellular rejection grade > or = 3A of the International Society for Heart and Lung Transplantation. We compared the levels of cytokines in the two groups.', 'Circulating IL6 levels were significantly higher when there was a low grade (0-2) cellular rejection in the biopsy versus the group of biopsies grade > or = 3A (19.8 +/- 27 versus 12.9 +/- 10 pg/mL; P = .001). An IL6 level higher than 30 pg/mL showed a negative predictive value of 95% for the presence of acute rejection grade > or = 3A.'] Are elevated levels of serum interleukin-6 associated with low grade cellular rejection in patients with heart transplantation?