Injectable hydrogels based on hyaluronic acid (HA) and poly(ethylene glycol) (PEG) were designed as biodegradable matrices for cartilage tissue engineering. Solutions of HA conjugates containing thiol functional groups (HA-SH) and PEG vinylsulfone (PEG-VS) macromers were cross-linked via Michael addition to form a three-dimensional network under physiological conditions. Gelation times varied from 14min to less than 1min, depending on the molecular weights of HA-SH and PEG-VS, degree of substitution (DS) of HA-SH and total polymer concentration. When the polymer concentration was increased from 2% to 6% (w/v) in the presence of 100Uml(-1) hyaluronidase the degradation time increased from 3 to 15days. Hydrogels with a homogeneous distribution of cells were obtained when chondrocytes were mixed with the precursor solutions. Culturing cell-hydrogel constructs prepared from HA185k-SH with a DS of 28 and cross-linked with PEG5k-4VS for 3weeks in vitro revealed that the cells were viable and that cell division took place. Gel-cell matrices degraded in approximately 3weeks, as shown by a significant decrease in dry gel mass. At day 21 glycosaminoglycans and collagen type II were found to have accumulated in hydrogels. These results indicate that these injectable hydrogels have a high potential for cartilage tissue engineering.