Poly(propylene fumarate-co-ethylene glycol) [P(PF-co-EG)] hydrogels were examined as in situ polymerizable carriers for endothelial cells. The temperature increase from 37°C during cross-linking was measured. The maximum temperature did not increase above 38.3°C for any copolymer formulation. The temperature profiles also appeared to be independent of the amount or molecular weight of poly(ethylene glycol). These materials were polymerized in situ in a subcutaneous rat model and evaluated for initial biocompatibility. A normal wound-healing response was seen with formation and subsequent maturity of a fibrous capsule. Endothelial cells were embedded in vitro during the cross-linking process and their proliferation was assessed over the first 24 h. There was significant DNA synthesis by the embedded endothelial cells during this time period. These data suggest that P(PF-co-EG) hydrogels could be developed for use as injectable cell carriers.