Erythrocyte sedimentation rate is normal in 20% to 25% of patients with discitis due to common pathogens. We evaluated serum amyloid A (SAA) protein and urinary trypsin inhibitory activity in osteoarticular infections comparatively with erythrocyte sedimentation rate and serum C-reactive protein in 20 patients including 14 with discitis due to common pathogens and 6 with septic arthritis. Assays were performed on D0, D8, D15, D30, and D60 after initiation of antimicrobial therapy. On D0, all four markers were significantly higher in patients with septic arthritis than in patients with discitis. C-reactive protein levels exhibited the fastest kinetics with a return to normal values within 15 days in both conditions. Urinary trypsin inhibitory activity was only slightly elevated in patients with discitis and returned to normal within 30 days in both conditions. Serum amyloid A levels required 30 to 60 days to return to normal. Erythrocyte sedimentation rate exhibited the slowest kinetics, with normal values being achieved only after 60 days. Although simple, rapid, and inexpensive, urinary trypsin inhibitory activity determination exhibits poor sensitivity. Serum amyloid A assay is not routinely available but may be a valuable parameter for monitoring patients whose erythrocyte sedimentation rate and C-reactive protein level are normal (as in 2 of our patients with discitis).