We generate a cloud of monodisperse binary droplets in a piston-expansion-tube by homogeneous nucleation and subsequent growth in a supersaturated vapor. By Mie light scattering we measure the growth rate of the droplets in the radius range from 0.16 to 3 mu m. We investigate the water-n-propanol system because the growth behavior of the pure substances is very well known from previous studies. Our model calculations are an extension of a successful unary model to the binary case inwhich the droplet composition is treated as a variable. The calculation starts at the nucleus, passes through the transition zone about Knudsen number one and extends to the final droplet/vapor equilibrium which is only reached when vapor depletion and heat release are taken into account. The model is in good agreement with the experimental data.