Hello Harry.

I thought you'd cracked it but no, I've transferred to code in the init and its still concatenating. Damn!

Really? What am I doing differently than you because this works for me. I droppped the customer and orders table from the TasTrade sqample app into the DE of a little form. I dropped 2 combos on the form. The first had a RowSourceType of 6-Fields and a Rowsource of Customer.Cust_id. I named this combo cboCust_id and put this code in its Valid:

Thisform.cboOrders.Requery()

This code in cboOrders.Init(). Note that the MESSAGEBOX() showed me that the length of the RowSource was 309:

lcRowSOurce = [SELECT Customer.Company, Customer.Contact, Customer.Country, ]
lcRowSource = lcRowSource + [Orders.to_name, Orders.to_address, Orders.to_city, Orders.order_date, ]
lcRowSource = lcRowSource + [order_amt FROM Orders JOIN Customer ON Orders.Cust_id = Customer.Cust_id ] 
lcRowSource = lcRowSource + [WHERE Orders.cust_id = Thisform.cboCust_id.Value ]
lcRowSource = lcRowSource + [ORDER BY order_date DESCENDING INTO CURSOR Junk NOFILTER]
MESSAGEBOX( 'Length of RowSOurce = ' + TRANSFORM( LEN( lcRowSource ) ) )
This.RowSource = lcRowSOurce

When I ran the form, everything was peachy keen and hunky dory with no truncation of the RowSOurce.