Whereas C-reactive protein (CRP), procalcitonin (PCT) and mid-regional pro-atrial natriuretic peptide (ANP) may be of use at the bedside in the management of adult patients with infectious disorders, their usefulness has not been established in the setting of acute pyelonephritis. To assess the effectiveness of CRP, PCT and ANP measurements in guiding emergency physicians' decisions whether to admit to hospital patients with acute pyelonephritis, we conducted a multicentre, prospective, observational study in 12 emergency departments in France; 582 consecutive patients were included. The reference standard for admission was defined by experts' advice combined with necessity of admission or death during the 28-day follow-up. Baseline CRP, PCT and ANP were measured and their accuracy in identifying the necessity of admission was analysed using area under curves (AUC) of receiver-operating characteristic (ROC) plots. According to the reference standard, 126 (22%) patients required admission. ANP (AUC 0.75, 95% CI 0.69-0.80) and PCT (AUC 0.75, 95% CI 0.71-0.80) more accurately predicted this than did CRP (AUC 0.69, 95% CI 0.64-0.74). The positive and negative likelihood ratios for each biomarker remained clinically irrelevant whatever the threshold. Our results did not support the use of these markers to help physicians in deciding about admission of patients experiencing acute pyelonephritis in daily practice.