Abstract: The invention concerns a novel adjustable roller pump assembly of the type comprising a semi-circular plate against the inner surface of which a flexible tube is located and a pair of diametrically arranged cylindrical rollers mounted on a driven rotatable body. The invention is related to a special means for adjusting the distance between the axes of the rollers so that the degree which the rollers compress the flexible tube can be adjusted. This means comprises an adjustment shaft rotatable about an axis transverse of the axis of rotation of the rotatable body and having at its ends cylindrical locating elements eccentric to the axis of rotation of the adjustment shaft, said locating elements acting on arms on which rollers are mounted so that adjustment of the adjustment shaft displaces the arms and hence the rollers.