Get rid of the where criteria, dont need it when using insert. Then give it all 4 fields and their values instead of only two. On phone so cant type out an example but ill check back later if you dont get it

What I want is that merge 2 IDs from left form to 1 ID in the right form. I changed the code but then it gave me error and I understand that because in the left I have only one field (Description) that goes to two fields in the right and the same with LotNr. Would you please correct me, thanks.

Youre going to need to use a checkbox and a recordset and a more complicated setup if you want to pick them out of a continuous form. If you just made two combo boxes to pick them from it could be simpler. Say you made Lot1Combo and Lot2Combo and it had the ID (Column 0), the Lot (Column 1), and the description (Column 2) in it. Then you could do something like this (assuming you are storing the string value of the lot and not an ID)

Currentdb.execute "Insert Into CockTailLotT (Antibody1,Lot1,Antibody2,Lot2) VALUES (""" & Lot1Combo.Column(2) & """,""" & Lot1Combo.Column(1) & """,""" & Lot2Combo.Column(2) & """,""" & Lot2Combo.Column(1) & """)"

Thanks a lot.