Betaine, also known as N,N,N-trimethyl glycine, is a soluble nitrogenous compound present at significant 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 significant 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 confirmed that betaine is present in large amounts in sugar-beet molasses (up to 6% w/w) and in the effluent of processes using sugar-beet molasses as substrate (up to 4.5 g dm(-3)). Betaine appeared to be almost completely degraded in the two full-scale anaerobic treatment plants sampled. This was confirmed 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.