A two-dimensional projection map was computed of the Ca2+-ATPase molecules in sarcoplasmic reticulum, isolated from rabbit skeletal muscle. Crystalline arrays of Ca2+-ATPase molecules were formed by incubating the membrane vesicles with phospholipase A2 and dialysing against Tris/HCl buffer. Ca2+-ATPase molecules appear as quasi-triangular blobs in the projection map and seem to form dimers. The projection map seems to indicate an enzyme conformation somewhat similar to vanadate-induced crystals but different from lanthanide-induced crystals of Ca2+-ATPase.