1. Two enzyme systems obtained from Pseudomonas FR capable of catalysing the alphabeta-elimination of L-serine O-sulphate exhibit a wide range of substrate specificity. Greatest activity was exhibited towards beta-substituted serine and cysteine derivatives. Enzyme A shows a marked preference for the L-isomeric form and enzyme B shows a preference for D-isomers. 2. The alternative activities were shown to be properties of the same enzyme by inhibition properties and heat denaturation experiments. 3. The assay of enzyme A by a number of alternative substrates at various stages during its purification confirmed the multi-substrate specificity of the system. 4. Growth of Pseudomonas FR on S-methyl-L-cysteine as the sole carbon source also resulted in the induction of enzyme B. Growth patterns and levels of induced enzyme were similar to those obtained when L-serine O-sulphate was employed in comparable circumstances.