These studies investigated the utility of calcium alginate as a biocompatible polymer matrix within which large numbers of chondrocytes could be held successfully in a three-dimensional structure and implanted. Further, the ability of chondrocyte-calcium alginate constructs to engraft and generate new cartilage was examined. Chondrocytes isolated from calf shoulders were mixed with a 1.5% sodium alginate solution to generate cell suspensions with densities of 0, 1.0, 5.0, and 10.0 x 10(6) chondrocytes/ml. The cell suspensions were gelled to create disks that were placed in subcutaneous pockets on the dorsums of nude mice. The alginate concentration and CaCl2 concentration used to make the disks also were varied. A total of 20 mice were implanted with 67 bovine chondrocyte-calcium alginate constructs. Samples with an initial cellular density of at least 5.0 x 10(6) chondrocytes/ml demonstrated gross cartilage formation 12 weeks after implantation. Cartilage formation was observed microscopically in specimens with a cellular density as low as 1.0 x 10(6) chondrocytes/ml. The histoarchitecture of the new cartilage closely resembled that of native cartilage. Cartilage formation was independent of CaCl2 concentration (15 to 100 mM) or alginate concentration (0.5% to 4.0%) used in gel polymerization.