Droughtmaster steers from the CSIRO Research Station at Lansdown, 50 km south of Townsville, Queensland, were assessed at slaughter for indications of leucaena toxicity and the presence of the 3,4 dihydroxypyridine (DHP)-degrading bacterium Synergistes jonesii. This bacterium had been introduced to the herd 25 years earlier. Absence of clinical signs of ulceration of the oesophagus, absence of DHP in the urine, the presence of normal thyroid glands and the ability of rumen fluid to degrade high levels of mimosine from leucaena shoot tips in vitro all confirmed that these steers had an active bacterial culture capable of degrading mimosine and its degradation products 3,4 and 2,3 DHP. Steers had been away from the Research Station and away from leucaena pastures for long periods but had clearly not lost the bacteria or if they had, they had regained them on return to leucaena pastures on Lansdown. It is postulated that the bacteria may spread via the faeces in cattle yards and remain in the rumen for long periods, even at low levels, in the absence of leucaena in the diet. Reasons other than the effectiveness of the bacterium should be explored to explain the failure of cattle in some Queensland herds to fully degrade 3,4 and 2,3 DHP.