[en] Reactor-production of ¹⁸F is mostly performed by ir irradiation of Li₂CO₃, the formation depending on the secondary activation reaction: ⁶Li(n, α)³H; ¹⁶O(³H, n)¹⁸F. The ¹⁸F then formed is carrier-free. In the present study reactor-irradiated Li₂CO₃ was extracted with water and the chemical form of the aqueous ¹⁸F-activity was investigated by paper chromatog tography. After aqueous dissolution of neutron-irradiated Li₂CO₃ more than 99% of the formed ¹⁸F is present as fluoride- ¹⁸F, as shown by paper chromatography. +he interference of Li has to be recognized. (T.G.)