Abstract: An aqueous suspension of pure 5-aminosalicylic acid adapted for rectal administration is rendered storage stable against color formation by storing the suspension in a single dose polyethylene bottle adapted for rectal administration of the suspension, in a substantially oxygen-free atmosphere and in the presence dissolved therein of up to about 0.25% of bisulfite and protecting the suspension from exposure to atmospheric oxygen during storage by sealing the plastic bottle, in a substantially oxygen-free atmosphere, in a plastic pouch having a low oxygen transmission rate.