Polycaprolactone (PCL) polymers which illustrate both biocompatibility and resorbability for replacement or bulking of damaged or diseased tissue are important in tissue engineering. Cytocompatibilty of these polymers was assessed on two-dimensional PCL disks and threedimensional PCL solid and PCL hollow microspheres using human uterine mixed leiomyosarcoma (SKUT-1) and hamster ductus deferens leiomyosarcoma (CRL-1701) cell lines. Possible PCL cytotoxicity and morphology were investigated in SKUT- and CRL-1701 cells. SKUT cells cultured in disk and microsphere extracts between 24 h and 5 day time periods displayed statistically increased metabolic activity, though activity decreased significantly on 1 month and 1 year extracts. However, the metabolic activity of CRL-1701 cells was similar to controls. Activity increased significantly on the 1 month extracts and decreased significantly on the 1 year extracts. Scanning electron microscopy illustrated increased cell density of cells attached to pre-conditioned disks. After 5 days, cells were spindle-shaped, following microspheres contours indicating high focal adhesion. Both cell lines migrated inside the hollow microspheres, indicating that they benefit from the sheltered environment. This in vitro study suggests that hollow microspheres allow for further cell expansion with a sheltered environment to protect cells from sheer stress experienced in vivo.