This in vitro study examined the marginal integrity of Class II lesions using three restorative techniques. Class II preparations (MO and DO) were placed in 30 teeth. Half had the cervical margin placed 1 mm below the CEJ, the remaining had cervical margins 2 mm above the CEJ. The preparations were randomly restored using three techniques: 1) Glass ionomer liner and posterior composite resin; 2) Glass ionomer silver cermet placed in the proximal box to the contact area and the remainder restored with posterior composite resin; 3) Glass ionomer silver cermet only. All 30 teeth were loaded with 17 kg, thermocycled and stored in 37 degrees C solution for 30 days. The teeth were again loaded, immersed in 2% basic fuchsin solution for 24 hours, sectioned and photographed. Microleakage was calculated, according to the depth of dye penetration. Results demonstrated Techniques 1 and 2 to have less marginal leakage than Technique 3 when preparations remained in enamel and Techniques 1, 2 and 3 when preparations were below the CEJ. The chi-square test indicated a statistically significant difference between restoration technique and marginal microleakage (P less than 0.001).