Eosin reacts with phenothiazine derivatives in dichloroethane to give intense fluorescent compounds having their excitation maximum at 318 nm and emission maxima at 450, 460 and 465 nm for prochlorperazine dimaleate, thiethylperazine dihydrochloride and trifluoperazine dihydrochloride, respectively. Under the optimum conditions, samples of 1-10 μg ml−1could be determined rapidly with coefficient of variation less than 1.8 %. This fluorescence reaction was also applied successfully to the determination of phenothiazine drugs in some pharmaceutical preparations.