What you describe (as I understand your wording) is two one-to-many relationships.
From your relationship graph, grab Patients:: PatID and drag it to Series::SerielID
Create a new field "Series::TreatmentID and grab Series::TreatmentID and drag it to Treatment::TreatmentID
This will let one patient relate to many series, and one series relate to many treatments.
If I assume correctly, you should then double click the relationship box and allow for new records to be created by this relationship in the respective "many" table but NOT allow creation of records in the respective "One" table.
(i.e. a series can create treatments, but a treatment cannot create a series).
Is this what you are after?
(Note, the space in Patients:: PatID should not be there...I had to put it in so it didn't look like Patients::PatID )
thanks! was unsure about this.... will try further and of course: I ordered a Manual Book for FM10.... :-))) thanks!!!!