Most of the simplest techniques needed for studying invasive stoats (Mustela erminea) in New Zealand were developed, all unknowing, during a preceding doctorate study of weasels (M. nivalis) in England, the native country of both species. Both retained their hard-wired genomes and natural behaviour during and ever since the transfer, so the procedures developed and problems solved in the 1960s turned out to be applicable (with a few modifications) to work on stoats throughout the 1970s and 80s. These included the following. Twice daily live trap inspections, 1 week in three; the best trap lure (rabbit scent renewed daily); white mouse bait to provide food for a captive, easily distinguished from natural prey in the scats; individual identification by ear-tags and belly patterns; field anaesthesia (required for handling and tagging); gut analyses; home range size and turnover; estimated impact on woodland rodents; incidence and cure of raiding nest boxes of titmice (Paridae); collecting large samples of carcases from professional trappers; routine carcase analyses; skull cleaning; age determination; life tables; mortality and survival rates; longevity; and pre-computer data analyses using edge-punched cards and simple non-parametric statistics. These data also help understand weasels in New Zealand which are too scarce to provide local information.