As part of Zoltan Kodaly's choral method available here are 77 Two-Part Exercises.

One hundred and seven Two-part exercises by Zoltan Kodaly based on the concept that singing is the most effective way of entering fully into the spirit of music and of understanding it. The theoretical studies for correct intonation in Let us Sing Correctly attempt to instill a natural intervallic approach to singing.

As part of the composer's Choral method available here are Zoltan Kodaly's 66 Two-Part Exercises.