Abstract: A differential ionometric cell containing an exchangeable TaF6- or F- ion-selective module was proposed for continuous-flow analysis. The TaF6--selective module was made from a plastic tube (i.d. 8 mm) comprising an ion-selective membrane electrode prepared from 10 mM tetradecylphosphonium hexafluorotantalate in dibutyl phthalate and PVC. The F--selective module was based on a EuF3-doped LaF3 monocrystal (diameter of 7 mm) contained in a fluoroplastic tube which was pressed in a poly(methyl methacrylate) block. Measurements were made vs. Ag - AgCl. The cell was used for determination of Ta in Ta(OH)5 (after conversion into TaF6- by evaporation with HF) and F in K2ZrF6 or NH4F. Working ranges were 0.5 to 1.5 mM Ta and 10 to 40 mM F. The coefficient of variation were 0.55 and 0.7% for Ta and F, respectively. Results for Ta are compared with those obtained by extraction - gravimetry. The output was 20 samples in 7 h.