The morphology of fissures occlusally was examined by splitting teeth along fissures; this split occurred from the base of the fissure and was checked by serial sectioning. The conclusion is that fissures tend to be an association of adjacent pits. Staining of teeth for fissure shape determination indicates a high presence of organic material in fissures and pits with stained pellicle between pits. The pellicle is often very evident on the lower inclines of cusps, in the region where retention is sought for sealants. In a second phase, an examination of a large number of extracted molars showed that the occlusal fissure extension buccally in lower molars and lingually in upper molars was nearly always interrupted by an enamel col between adjacent cusps. Grooves occlusally or axially adjacent to fissures are often surfaced with stained pellicle. This may be mistaken on visual examination without magnification as extensions of fissures.