A segregationally stable host-plasmid system, E. coli DH5 alpha (pTKW106), was used to study the effect of induction on the accumulation rate of cells and gene expression in biofilm cultures. Isopropyl beta-D-thiogalactoside (IPTG) was used to induce the expression of beta-galactosidase from the plasmid. The biofilm cell net accumulation rates decreased with increasing induction levels. At 0.17 and 0.34 mM of IPTG, the biofilm cell net accumulation rates ranged between 17 and 30% when compared to the uninduced case. At 0.51 mM of IPTG, the biofilm cell density never increased. At 0.17 and 0.34 mM of IPTG, beta-galactosidase contents reached maxima 36 hours after induction with both amounts representing about 7.5% of total protein. At 0.51 mM of IPTG, beta-gatactosidase production reached its maximum, about 16% of total protein, 48 hours after induction. The beta-galactosidase mRNA synthesis rates increased with increasing inducer levels. Maximum beta-galactosidase mRNA synthesis rates were reached 36 hours after induction for each IPTG concentration.