This randomized, double-masked, placebo-controlled clinical trial evaluated the effect of enamel matrix derivative (EMD) on clinical and radiographic parameters of periodontal intrabony defects. A split-mouth design was used in 16 chronic periodontitis patients who had similar defects (> or =6 mm of probing depth). Both groups underwent scaling and root planing and were acid-etched with EDTA. The test sites received the EMD solution and the controls a placebo. Clinical examinations of all 16 patients and radiographs of 14 patients were available at baseline and 6 and 12 months after surgery. Clinical outcomes included probing depth (PD) and clinical attachment level (CAL); radiographic analysis was performed using computerized linear measurements. Intergroup comparisons were performed by paired samples t test, and over time comparisons were made by general linear model (alpha = 0.05). A statistically significant improvement over time for PD and CAL and a decrease of the vertical component of the defect was detected in both groups. Comparisons between groups revealed at baseline a mean+/-SD value of CAL of 12.93+/-2.00 and 13.47+/-2.93 for test and control groups, respectively. These values decreased to 10.92+/-1.92 and 11.31+/-1.86 after 12 months for test and control. No statistically significant differences could be observed between groups. PD displayed similar results from 7.57+/-1.02 and 7.38+/-1.16 for test and control groups at baseline to 3.40+/-1.82 and 2.99+/-1.07 after 12 months. If the data are divided into smokers and non-smokers, no differences are observed. Use of EMD did not result in more improvement in clinical and radiographic parameters compared to the placebo.