The origin, expression and role of matrix modifying enzymes in dental enamel was investigated by zymography and growth of enamel crystals in vitro. Gelatinase activity of the neutral metalloprotease type was detected at similar molecular weights in enamel organ, enamel and dentine. The activity was present throughout all developmental stages in enamel organ but was dramatically reduced in the maturation stage of the enamel. Activity of the serine protease type directed against enamel matrix was also detected in enamel, particularly in the maturation stage. No such activity was detected in the enamel organ. Phosphatase activity at alkaline pH was demonstrated at similar molecular weights in both enamel and enamel organ. This activity was maximal in the maturation stage. Further experiments showed that both serine proteases and alkaline phosphatase were able to facilitate enamel crystal growth in vitro. Matrix modification via temporally and spatially restricted enzymes may be directly involved in the control of enamel crystal growth and hence in the determination of final tissue architecture.