Combine sugar, salt and cornstarch; add water and grapefruit juice and cook slowly, stirring constantly, until thick. Simmer 5 minutes, add butter and egg yolks and remove from heat. Beat well; cool.

Turn into pastry shell. Beat egg whites until stiff, add sugar slowly and stir in grapefruit juice. Cover top of pie with meringue and bake in a 300 degree oven for 10 to 15 minutes or until meringue is browned lightly. Makes 1 (9 inch) pie.