A modular trough has been designed to facilitate both classical LB techniques and those developed initially by Montal and Mueller for the study of biomolecular membranes. The trough is a development of the ’diamond design’ previously reported. The barriers can vary the surface area between 115 cm2 and 17.5 cm2 in a design deliberately made small to achieve a low subphase volume of about 550 cm3. The latter is important (because of cost) when working with biomolecules that are soluble in the subphase. In the Montal-Mueller mode the design facilitates control of surface pressure. The surface flow is channelled by shoulders to produce near-normal flow at an LB substrate, and high quality films are produced.