The cytocompatibility of amphiphilic, thermoresponsive and chemically crosslinkable macromers was examined in vitro. Macromers synthesized from pentaerythritol diacrylate monostearate, N-isopropylacrylamide, acrylamide and hydroxyethyl acrylate in different molar ratios and with varying molecular weights and lower critical solution temperatures were evaluated for cytocompatibility with rat fibroblasts. Cell viabilities of over 60% for all and over 80% for most formulations were observed after 24-h incubation with macromers with molecular weights in the range of approximately 1500-3000 Da. The chemical modification of the macromers with a (meth)acrylate group was shown to have a time- and dose-dependent effect on cell viability. Uncrosslinked macromers with lower degrees of (meth)acrylation allowed for cell viability of over 60% for up to 6 h. (Meth)acrylated macromers with lower critical solution temperature (LCST) closer to physiological temperature allowed for higher cell viabilities as opposed to those with lower LCST. The data suggest that when the (meth)acrylated macromers are assembled into a physical gel, their cytotoxicity is diminished. After gel phase separation, cytotoxicity increased. This study gives information on the parameters that enable viable cell encapsulation for in situ forming hydrogel systems.