The myxoma of the jaws represent 8% of the odontogenic tumours in our series (324 cases). The 5 cases described here were studied by histoenzymological and electron microscopic methods. The first method demonstrated in the majority of tumoral cells a high level of activity of alkaline phosphatases and ATPases similar to that noted in odontoblasts of the dental pulp. In addition, an acid phosphatase activity was also present in numerous cells but usually at a low intensity. Ultrastructurally, the tumour was composed of 3 main cellular types: young round cells with numerous ribosomes; stellate secretory cells with well-developed granular ergastoplasma and Golgi apparatus; fusiform cells with characteristics of fibroblasts. Some macrophages and myofibroblasts were also present. The intercellular substance was granulofilamentous and in one of our cases calcifications were obvious upon some collagen fibers. All these results seem to corroborate the hypothesis of odontogenic nature of the tumour. Early odontogenic induction induces the transformation of fibroblasts into cells with enzymatic activities similar to those of odontoblasts and the calcification of collagen fibers seen in one of our cases would express an early mineralization.