Hi All. (Just to stem the growing tide of helpful replies pointing out my stupidity). It as as everyone suspects - I have at some point saved my workspace so there is a .Random.seed lurking. This is something I don't normally do, hence haven't encountered this before... it also explains why running my older R versions doesn't show this behaviour. Thanks for the prompt responses, virtual beers to all. C -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Dr. Carl Donovan Research Fellow in Statistical Computing Ph +44 1334 461802 The Observatory Buchanan Gardens University of St Andrews St Andrews Fife KY16 9LZ Scotland