This work investigates the cytocompatibility of several photoinitiating systems for potential cell encapsulation applications. Both UV and visible light initiating schemes were examined. The UV photoinitiators included 2,2-dimethoxy-2-phenylacetophenone (Irgacure 651), 1-hydroxycyclohexyl phenyl ketone (Irgacure 184), 2-methyl-1-[4-(methylthio) phenyl]-2-(4-morpholinyl)-1-propanone (Irgacure 907), and 2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone (Darocur 2959). The visible light initiating systems included camphorquinone (CQ) with ethyl 4-N,N-dimethylaminobenzoate (4EDMAB) and triethanolamine (TEA) and the photosensitizer isopropyl thioxanthone. A cultured fibroblast cell line, NIH/3T3, was exposed to the photoinitiators at varying concentrations from 0.01% (w/w) to 0.1% (w/w) with and without the presence of initiating light. The results demonstrated that at low photoinitiator concentrations (< or = 0.01% (w/w)), all of the initiator molecules were cytocompatible with the exception of CQ, Irgacure 651, and 4EDMAB which had a relative survival approximately 50% lower than a control. In the presence of low intensity initiating light (approximately 6 mWcm(-2) of 365 nm UV light and approximately 60 mWcm(-2) of 470-490 nm visible light) and initiating radicals, Darocur 2959 at concentrations < or = 0.05% (w/w) and CQ at concentrations < or = 0.01% (w/w) were the most promising cytocompatible UV and visible light initiating systems, respectively. To demonstrate the potential use of cytocompatible photoinitiating systems in cell encapsulation applications, chondrocytes were encapsulated in a photocrosslinked hydrogel using 0.05% (w/w) Darocur 2959 (cytocompatible) and 0.01% (w/w) Irgacure 651 (cyto-incompatible). After photopolymerizing for 10 minutes with approximately 8 mWcm(-2) of 365 nm light, nearly all the chondrocytes survived the process with Darocur 2959 while very few of the chondrocytes survived the process with Irgacure 651.