The degradation of trimethylammonium compounds that are structurally related to y-butyrobetaine and D,L-carnitine has been examined with variously grown resting cell suspensions of Acinetobacter calcoaeeticus and Pseudomonas putida. Ac. calcoaceticus grown on either 7-butyrobetaine effectively degraded o,I~-3-fluoro-4 N-trimethylaminobutyric, 4-N-trimethylaminocrotonic and 5-N-trimethylaminopentanoic acids with stoichiometric formation of triylaminopentanoic acids with stoichiometric formation of trimethylamine. None of these betaine analogs was metabolized by Ps. putida grown on D,L-carnitine as sole source of carbon. Only D,L-carnitine-grown Ac. calcoaceticus showed a slow but significant utilization of D,L-3-chloro-4-N-trimethylaminobutyric acid with equivalent formation of trimethylamine. Neither Ac. calcoaceticus nor Ps. putida, grown on either 7-butyrobetaine or D,L-carnitine as sole source of carbon degraded any of the following quaternary ammonium compounds: glycinebetaine, N-trimethylethanolamine-Ophosphate, N-trimethylett~anolamine-O-sulfate, 3-N-trimethylaminopropanol, 3-N-trimethylaminopropionitrile, 3-Ntrimethylaminopropionic acid, 3-N-trimethylaminopropane sulfonic acid and 6-N-trimethylaminohexanoic acid. Cleavage of the C-N bond of 4-N-trimethylaminocrotonic acid, and lack of stereochemical specificity with respect to the configuration at C-3 for the other betaines undergoing a similar degradation with formation of trimethylamine, are inconsistent with a mechanism involving a simple Hofmanntype of elimination reaction.