I'm following up on this idea that I posted to describe how we've attempted to work around this limitation in the API to do an AND query on constituent attributes.  As background, we are a company that uses RE/BBNC to support many fraternity/sorority chapter alumni associations.  We segment our clients by use of constituent code (which indicates fraternity/sorority), and use the constituent attribute to indicate the chapter (this is the actual client).  This structure has worked really well for us in RE and BBNC.  The example I've already given where we we want to find members where they have a custom field category client code=123 (this is the chapter client) AND custom field category status=alumnus (we want to both  return a count when these conditions are true and display constituent data for viewing), What we did was 1) run the query where custom field category client code=123 - this returned something like 2,000 results (easy enough), we then attempted to extract responses from a  query where custom field category status=alumnus (our intention was to then to compare the lists using our own tools to find where the parent ids matched between the two, giving us the union for this unique client).  However, the API times out on giving us all the results for this second set of data (about 100K records). So this work around simply does not work.  We've thought of doing some creative recoding of records to get around this limitation (such as creating unique custom field CATEGORIES  that are concatenations of custom field categories and values - As in categories 123Alumunus, 123Expelled, 123Undergraduate; etc. but this is so incredibly clunky and would require adding about 500 unique  custom field CATEGORIES to accommodate all clients with a website we host for them. Besides being unwieldy, it completely defeats the original structure and purpose of custom field categories/values. I don't want to go down this cumbersome/complicated path if the API can be modified to allow multiple searches as described on constituent custom fields.