Betaine, also known as N,N,N-trimethyl glycine, is a soluble nitrogenous compound present at signi®cant concentrations in sugar-beet molasses. Molasses is used as substrate in a wide range of industrial fermentations, for example, alcohol, acid and yeast cell production. Betaine is not consumed to any signi®cant extent during these fermentations and appears to largely pass through the subsequent processing stages, becoming an important constituent of the wastewater produced by these industries. The present study con®rmed that betaine is present in large amounts in sugar-beet molasses (up to 6% w/w) and in the ef¯uent of processes using sugar-beet molasses as substrate (up to 4.5 g dm À3 ). Betaine appeared to be almost completely degraded in the two full-scale anaerobic treatment plants sampled. This was con®rmed by anaerobic activity tests performed with both acclimated and unacclimated anaerobic sludge. The results obtained suggest the possible involvement of a multistep degradation process, with the likelihood of a nitrogen-containing intermediate. Finally, although not totally discountable, betaine degradation does not appear to be coupled to sulfate reduction during treatment of high-sulfate wastewaters.