Possible roles of the cellular messenger nitric oxide (NO) in post-mortem meat ageing were investigated in bull m. longissimus lumborum. Both enhancement and inhibition of NO activity had positive and negative effects, respectively, on early rates of ageing. These also correlated with direct measurements of NO in the meat samples. However, by 8 days of storage, the tenderness was not significantly different to non treated meat samples. (C) 1997 Elsevier Science Ltd. All rights reserved.