Assessment of activity of lupus nephritis is critical in the management and ultimate prognosis of patients. Clinical and laboratory data of 18 children with lupus nephritis were examined to determine what factors reflect activity of renal lesions. Using a histologic scoring system with an activity index (AI) and a chronicity index (CI), correlations between histologic scores and laboratory parameters were analyzed. Serum total protein, albumin and complement at the time of renal biopsy inversely correlated with the AI, but not parameters correlated with the CI. Serum complement levels correlated inversely with the amount of glomerular immune deposits, while the AI and CI correlated with the amount of immune deposits. These results suggest that hypoalbuminemia and hypocomplementemia are indicators of severe, active lupus nephritis, pointing to the need for early renal biopsy and intensive therapy.