Deep CCD images have revealed a population of faint blue galaxies which have a high surface density. In an Einstein-de Sitter universe, the observations require that these galaxies have a higher space density and are less strongly clustered than normal luminous galaxies observed at the present day. We use a series of N-body simulations to show that in a hierarchical theory of galaxy formation, such as the cold dark matter model, these observations can be explained if the faint blue galaxies are a transient population associated with dark haloes of low masses and circular speeds (M(H) less than or similar to 10(12) M., v(c) less than or similar to 100 km s(-1)).