Four bacterial strains (tentatively identified as strains of Aeromonas, Pseudomonas, Flavobacterium and Bacillus) isolated from contaminated metal-working fluids were assayed for the capacity to utilize the borate derivatives of monoethanolamine (MEA), diethanolamine (DEA) and triethanolamine (TEA). Two of these strains, isolates AV1 (Flavobacterium) and CL1 (Bacillus) were capable of growth on each of the borate esters with cell yields of 0.6 gl - 1 for AV1 cultured on DEA- and TEA-borate, 0.3-0.4 gl - 1 for CL1 cultured on DEA- and TEA-borate and approximately 1.4 gl - 1 for AV1 and CL1 cultured on MEA-borate. In the case of strain CL1, growth yields on TEA- or DEA-borate as substrates were doubled by the addition of potassium ions. Lower ethanolamines, glycolaldehyde, acetaldehyde and ammonia were identified as breakdown products. The enzymes produced during growth upon the alkanolamine borates were shown to possess similar properties to those seen for cells cultured upon alkanolamine hydrochlorides.