A least-squares refinement of x-ray diffraction data has been developed in which the parameters are the populations of atomic orbital products describing the molecular electron density distribution. The procedure is applied to alpha-oxalic acid dihydrate and cyanuric acid. Complementary structural information obtained by neutron diffraction has been used. In the absence of complementary information, the method allows simultaneous determination of structural and charge-density parameters. There is an indication of a migration of charge from the ppi to the psigma orbitals in both molecules.