Desorption of atropine sulphate and hyoscyamine hydrobromide by antacids such as magnesium trisilicate, magnesium oxide, aluminium hydroxide an bismuth carbonate was carried out i vitro. This was achieved by preparing a complex of the alkaloids with bromothymolblue and then partitioning th complex between aqueous buffer phase and non-aqueous chloroform phase. The latter was analyzed colorimetrically. The desorption followed the sequence: magnesium trisilicate greater than bismuth carbonate greater than aluminium hydroxide greater than magnesium oxide. The results also show that desorption is dependent on the amount of alkaloid adsorbed and the pH of the medium.