Langmuir-Blodgett films of a benzothiazolium styryl dye containing a 1,10-dithia-18-crown-6 ether group have been built-up from aqueous subphases of differing pH. The kinetics of the chromoionophore aggregate formation in a bilayer immersed in acidic water have been studied by absorption spectroscopy. Aggregation has also been found to occur in floating monolayers on an acidic subphase. The aggregates exhibit red-shifted absorption peaks and may be broken down by complex formation with Ag+ cations in water.