Two methods of investigating the surface rheological properties of spread monolayers are presented. Surface shear relaxation is capable of giving the relaxation spectrum over a wide range of frequencies but will only give a rough estimate of the strain. Surface resonance rheometry was used at a fixed frequency but with an accurately defined strain. Results are presented for monolayers of several materials and the effects of subphase pH, ions and temperature have been obtained and are discussed. Of particular significance to the Langmuir-Blodgett process is the discovery of a viscosity limit above which monolayer deposition is not successful. The viscosity of a monolayer can be controlled by adjusting the pH of the subphase (particularly if there are subphase divalent ions present) and we have used this control successfully to deposit a copper-containing docosanoic acid film.