Originally written for piano, in the period 1930-1941. Villa-Lobos orchestrated the work in 1942.
Orchestral version:2 Flutes +1 picc, 2 oboes +1 English Horn, 2 Clarinets +1 Bass Clarinet, 2 Bassoons +1 Contra Bassoon - 4 Horns, 3 Trumpets, 3 Trombones, 1 Tuba - Timpani, 3 Percussion players (BD, tam-tam, xylo), Celesta, Strings
This comprehensive listing of Bachianas Brasileiras scores from the Major Orchestra Librarians' Association website contains lots of useful information.
This work is one of the most popular works in the Villa-Lobos catalogue. Performances in the Villa-Lobos Concerts database (nearly 200 as of November 2011) are more or less evenly divided between the piano and orchestral versions.