The Wertheim method is applied to the calculation of thermodynamic and structural properties of a fluid that undergoes a reversible dimerization reaction a + b --> ab. The a and b particles are hard spheres with a single sticky spot that allows a,b dimerization, but no additional association. For this mixture of a's, b's and ab particles, one can add the direct correlation functions to the list of previously calculated quantities, such as the pressure, and the contact values of the pair correlation functions.