Abstract: The principles and techniques of flow injection analysis are illustrated by means of phosphate and SO2 determinations in fruit juice. Phosphate is determined by use of ammonium molybdate followed by reduction of molybdophosphate to the molybdenum blue with SnCl2. The determination of SO2 is carried out at pH >7 to dissociate any compounds formed between SO2 and other components in the juice. The SO2 is then allowed to diffuse through a PTFE membrane into a gas diffusion cell where it is treated with p-rosaniline - formaldehyde, and the resulting color change is measured at 580 nm. Possible applications for flow injection determination of other substances, e.g., ascorbic acid, Cl-, glucose, hesperidin, Mg, Ca, lactic acid, NO2-, NO3-, D-sorbitol, SO42-, ethanol and NH3-N, are tabulated. Analyses were carried out with a microprocessor-controlled flow injection analyzer. type 5020 (Tecator).