So I have a new theory about this. Searching for 'pdp-11' causes eBay to automagically limit the search to the 'Vintage Computing' category. They must have a keyword->category database. Anyway, if I manually then select 'All' categories, I get the same results for searches for both 'pdp-11' and 'pdp-11 pdp-11'. So my theory is that 'pdp-11 pdp-11' _doesn't_ hit their database, and so it goes to 'All' - thereby producing different results. So I just have to hit 'All' every time I do a search... Noel