Cells of Serratia marcescens, immobilized by entrapment in calcium alginate beads, were cultivated in two different media : a dairy waste (whey) and a complex medium (TYE). A study of the stabilization of the support employed was carried out after establishing the relationship existing between the degree of leakage from the support and the internal biomass, as well as the possible interactions between the substrate and the gel. In order to ascertain these facts, visual methods had to be developed to evaluate the number of breakages and relate these with the culture characteristics. Finally, repeated cycle cultures were carried out, establishing the evolution of product yields and the number of breakages on the support surface, showing the behaviour on whey in relation to the complex medium.