It is known that daily polyaspartic acid (PAA) protects the kidney from gentamicin nephrotoxicity in a standardized rat model despite marked cortical accumulation of the aminoglycoside. The present experiments address the duration of PAA protection. When administered every other day, PAA provided functional and histologic protection against gentamicin-induced toxicity. A stepwise reduction in nephroprotection occurred as the dosage interval was prolonged.