The second-harmonic intensity from alternate-layer Langmuir-Blodgett films of a coumarin dye, 4-[2-(7-diethylamino-2-oxo-2H-benzopyran-3-yl)ethenyl]-1 -octadecylquinolinium bromide, and an inert spacer, 1-octadecyl-4-methylquinolinium bromide, increases quadratically with the number of active layers. The optimum effective second-order susceptibility, albeit resonantly enhanced, is the highest to date for a thick alternate-layer film with chi(eff)((2)) = 190 +/- 30 pm V-1 at 1.064 mu m. The thickness and the real and imaginary components of the dielectric permittivity from the surface plasmon resonance at 532 nn are iota = 4.6 +/- 0.4 nm bilayer(-1), epsilon(r) = 2.4 +/- 0.2 and epsilon(i) = 0.8 +/- 0.2.