Aston and Craig's solution is so easy (de-activated Auto Filter, then control-A to select all data in the spreadsheet, and then re-activate the Auto Filter), and fixed my problem immediately (though I have less than 1,000 rows of data, which I believe is the threshold of Excel 03's capacity for filtering data. Thanks both for this simple, non-techie solution! (For some reason I cannot fathom, my excel was previously only allowing me to filter up to row 534, so my selected filter subject PLUS every row from 535 onward would show up in the spreadsheet, but thankfully it is now working correctly again!). Cheers all!