To investigate the in vitro degractability and cytotoxicity of long alkyl cyanoacrylate polymers [polycyanoacrylates (PCAs)], we synthesized five kinds of alkyl cyanoacrylates (ethyl, 2-octyl, n-octyl, ethylhexyl, and ethyl cyanoacryloyllactate). In vitro degradation in buffer solutions and cell cultures for cytotoxicity were performed with PCAs prepared by various polymerization methods. Lower alkyl homologues such as ethyl cyanoacrylate revealed a higher tissue toxicity than higher alkyl homologues. The amounts of formaldehyde released from various PCAs were not proportional to the rate of degradation. The apparent form of the cyanoacrylate polymers greatly affected the degradation rate, as the powdery polymers degraded much more quickly than the films. A new biodegradable polymer, prepared from ethyl 2-cyanoacryloyllactate, degraded more quickly than the others. The amount of formaldehyde released from the polymer degradation was high because it degraded rapidly. It was observed from cell culture experiments that the viability of the cells was higher with a lower release of formaldehyde because the alkyl side groups were bigger. Therefore, octyl cyanoacrylate polymers demonstrated lower amounts of formaldehyde by degradation and higher cell viability, and these monomers may be desirable for use as tissue adhesives. (C) 2003 Wiley Periodicals, Inc.