The biodegradation of 2-, 3- and 4-nitrotoluene was investigated in a simple laboratory test. All three isomers are shown to be biodegradable in a die-away test after adaptation of the inoculum, though different results were obtained with different types of activated sludges used as inoculum in the static test. The adaptation procedure, employed in this study, was a modification of a test method described by Pitter in 1976. It appeared that adaptation in a semi-continuous activated sludge system was most successful when a composite sludge was used consisting of activated sludge from a communal sewage plant and an extract of river mud. meta-Nitrotoluene was more resistant to attack by a mixed population of aquatic micro-organisms than the other isomers. The procedure used in this study is proposed as an attractive alternative for those methods which are recommended by the OECD and the EEC, to test the so-called 'inherent biodegradability'.