A preconcentration method is described for a flow-injection spectrophotometric determination of phosphate at the ng g^-1 level in sodium chloride. Coprecipitation and flotation were successfully achieved in 200ml of a 30%(w/v) sodium chloride solution at pH 8.5, with flocculent hydrated aluminum oxide precipitates (10mg as aluminum), 6mg of sodium oleate and 2mg of sodium dodecylbenzenesulfonate. Recoveries greater than 95% of phosphate were obtained with preconcentration coefficients higher than 103. The time required for the entire procedure was ca. 70min.