Discoid coralla of the solitary free-living reef coral Fungia scutaria were cut with a rock saw and rejoined in various paired combinations and orientations of autogeneic sections (self to self), isogeneic sections (clone-mate to clone-mate), and allogeneic sections (two different genotypes). Results of these experiments provide the first evidence of histocompatibility in a solitary coral. Autogeneic or isogeneic sections of coralla with one section containing a mouth were joined along cut edges. In all cases, fusion of tissues occurred within weeks, followed by skeletal fusion within months. However, autogeneic or isogeneic sections rejoined along the uncut edges did not fuse. Isogeneic pairings between two sections with mouths produced neither tissue/skeletal fusion nor cytotoxicity at the interface. Individual cut sections were allowed to regenerate. Sections containing the parent mouth did not develop new mouths. However, cut sections lacking a mouth always regenerated multiple mouths along the cut edge, but not along the uncut edge. Sections without mouths cut along a second line parallel to the first cut always regenerated mouths along the cut edge located closest to what had been the mouth area of the original corallum. The new mouths eventually developed into individual polyps.