The formulation and in vitro evaluation of a raft-forming antacid suspension using a natural dietary fibre, isapgol (Plantago ovata) husk, along with sodium bicarbonate and aluminium hydroxide, is described. The effect of various formulation variables on the neutralisation profile was determined by a static neutralisation test and simulated in vivo neutralisation was determined using the modified Rossett-Rice test. Raft strength was measured using the Steven's LFRA texture analyser. Rheological determinations were also carried out. A comparative in vitro evaluation with a marketed alginate/antacid formulation ‘Acigon’ indicated that isapgol can be successfully used in the formulation of a 'raft-forming antacid suspension.