The Lintzel method of trimethylamine oxide determination was found to give low results when less than 2 to 5 mg. oxide nitrogen was present. By suitable modification this could be reduced to 2 mg. above which a constant 96 per cent recovery was obtained. However, many fish extracts contain only 0.5 to 2 mg. nitrogen in the aliquot which can be used for the reduction.A modified Norris and Benoit procedure, which is much simpler to use, was developed. This gave about 96 per cent recovery down to about 0.4 mg. nitrogen. Extraction of the fish muscle with either trichloracetic acid or formaldehyde was satisfactory.