An upflow packed-bed cell recycle bioreactor (IUPCRB) is proposed for obtaining a high cell density. The system is comprised of a stirred tank bioreactor in which cells are retained partially by a packed-bed. $A;1.3;cm;(ID);{ imes};48;cm$ long packed-bed was installed inside a 2L bioreactor (working volume 1 L). Continuous ethanol fermentation was carried out using a 100 g/L glucose solution containing Saccharomyces cerevisiae (ATCC 24858). Cell retention characteristics were investigated by varying the void fraction (VF) of the packed bed by packing it with particles of $0.8{sim}2.0;mm$ sized stone, cut hollow fiber pieces, ceramic, and activated carbon particles. The best results were obtained using an activated carbon bed with a VF of $30{sim}35%$. The IUPCRB yielded a maximum cell density of 87 g/L, an ethanol concentration of 42 g/L, and a productivity of 21 g/L/h when a $0.5;h^{-1}$ dilution rate was used. A natural bleeding of cells from the filter bed occurred intermittently. This cell loss consisted of an average of 5% of the cell concentration in the bioreactor when a high cell concentration (approximately 80 g/L) was being maintained.