Some new data on the adduct of SF4 with BF3 are reported and arguments are given, based on these and other data, to indicate that the adduct is quite unlikely to be a donor-acceptor complex. Infra-red examination proved inconclusive due to the instability and reactivity of the adduct. SF4 has been found to react with F2 producing SF6 but is unreactive toward BrF3 and Cl2. It reacts rapidly with BCl3