L-Serine-degrading activity could be suppressed by controlling the methanol concentration in L-serine synthesis using resting Hyphomicrobium sp. NCIB10099 cells. Fifty-three mg/ml of L-serine were produced from 100 mg/ml of glycine and 104 mg/ml of methanol. It is believed that L-serine-degrading activity contributes to the reverse serine hydroxymethyltransferase reaction.