The dissociation and recombination of moderately complex molecules in a background of inert atoms has been investigated using a master equation with transition probabilities and spontaneous decayrates obtained from the statistical theory of reaction rates. A relatively simple expression has been derived for the steadystate dissociation rate constant which is valid at all pressures for molecules containing three or more atoms. This expression has been used with reasonable success to correlate the available experimental data for 21 molecules having from three to six atoms.