To clarify the biological characteristics of uterine leiomyomas, cells explanted and cultured from uterine leiomyomas and from normal myometrial tissue were observed by time-lapse cinemicrography and phase-contrast microscopy. The histological characteristics were evaluated by electron microscopy and immunofluorescence microscopy, and these observations revealed significant differences. By time-lapse cinemicrography, the cells cultured from leiomyomas and myometrium differed in their behaviour. Cells from the myometrium started to grow in parallel with the cell's major axis and formed topographically uniform hills and valleys by day 21 of culture. In contrast, the cells from leiomyomas started to grow irregularly, as if having no contact inhibition, and formed ball-like aggregates of cells by day 21 of culture. The aggregates resembled the nodules of leiomyoma in vivo. Ultrastructurally, cells from both leiomyomas and myometrium had typical features of smooth muscle. Immunofluorescently, a different distribution of alpha-smooth muscle actin-positive filaments and different staining of cellular fibronectin and N-cadherin between the cells from leiomyomas and myometrium were observed, which may contribute in part of the different behaviour of the cells. Given that the explant cell culture system resembles the features of uterine leiomyomas in vivo, this suggests that it can be used as an in-vitro model.