Cellular aggregates were prepared using biodegradable porous microspheres for injectable reconstruction of soft tissues in vivo. Biodegradable porous microspheres with sizes of similar to 50 mu m were prepared by a porogen leaching-phase separation process in an oil-in-water single-emulsion method using poly( D, L-lactide-co-glycolide). 3T3 L1 mouse preadipocyte cells were transformed into cellular aggregates by suspension cultivation in a spinner flask using the porous microspheres as effective buoyant and cell-adhesive microcarriers. Spherically shaped aggregates were readily formed with sizes of up to 1000 mu m with a higher number of viable cells compared to the nonporous microspheres. The resultant cellular aggregates exhibited far better extent of differentiation into adipocytes than the cell aggregates prepared from nonporous microspheres or monolayer cultured cells. The cellular aggregates could also be injected into nude mice using a syringe needle for adipose tissue regeneration in vivo. Immunohistochemical studies showed that the aggregate-derived tissues with porous microspheres displayed histological characteristics similar to adipose tissues 4 weeks after injection.