A simple query for ["A" or "B" or "C"] against a KeywordIndex containing 27k objects is taking about 7 seconds on a Celeron 1.6Ghz, which seems an absurdly long time to me. The bit of the operation that is taking the time is the part of the index which does a union of the results of each of the 3 query parameters. Reproducing this BTree union operation outside Zope in a unit test takes milliseconds. Very occasionally it takes milliseconds inside the KeywordIndex too. Something to do with memory usage perhaps? I'll continue looking into it. But main the reason I'm posting is to wonder if there any reason not to use the multiunion operator instead of the union operator in UnIndex.py... it should be faster, right? It seems a touch faster in some informal tests. Seb