Rat adjuvant arthritis (AA) was used as a model to evaluate several blood markers as possible predictive indicators of drug efficacy. AA was induced in Sprague-Dawley rats by the injection of complete Freund's adjuvant into the right hind foot pad. The rats were dosed p.o. from day 18 to day 31 with levamisole (10 mg/kg), indomethacin (1 mg/kg), diclofenac sodium (0.5 & 1 mg/kg), and prinomide (10 & 20 mg/kg). Disease severity was assessed by paw circumference on day 31. The following blood markers were analyzed: hyaluronate by ELISA, prostaglandin E2 by RIA, ESR by micro-dispette, total PMN by Technicon H-1, and albumin by BCG dye. Blood marker correlation (r) to disease severity was: hyaluronate (0.71), prostaglandin E2 (0.58), ESR (0.52), PMN (0.58), and albumin (-0.71). The relative rank order of drug efficacy (indomethacin, diclofenac sodium, and prinomide) did not differ using the change in paw circumference (day 31-day 17) or blood markers. Levamisole exacerbated the disease as measured by all the above parameters. Thus, these blood markers provide additional information for the statistical evaluation of drugs in rat adjuvant arthritis.