Adaptability of two amalgams--the dispersed-phase Dispersalloy and the spherical-particle-type Sybralloy--to cavity walls in a Class II cavity preparation was investigated. Four techniques for finishing cavity walls were compared, as was the adaptability of alloys at different occluso-gingival levels. The issues were examined by direct measurement of microleakage between cavity wall and the amalgam without the use of cavity varnish. There was no statistically significant difference in the adaptability of the two amalgams directly to the cavity walls, except those finished by a sharp hand instrument (hatchet) and restored with Dispersalloy. This combination demonstrated the best overall adaptability of amalgam to cavity walls. Sybralloy demonstrated best adaptability to walls finished with sandpaper discs. Although not significant, the gingival 1/3 of the Class II cavity preparation had more microleakage than the middle 1/3 or the occlusal 1/3, suggesting greater potential for recurrent decay. Overall dispersalloy demonstrated significantly better adaptability than Sybralloy.