Secretory granules, isolated from bovine neurohypophyses on isoosmolar Percoll‐sucrose‐EGTA gradients had a calmodulin content of 0.09 ± 0.01 μg/mg protein (SE, n = 6). The distribution of calmodulin on the gradient showed that it did not copurify with the granules. Specific binding sites for calmodulin with a high affinity (K_d = 2.43 ± 0.27 × 10^‐9 M (SE, n = 5)) and a maximum binding capacity of 1.3 ± 0.4 pmol/mg protein (SE, n = 5) could be demonstrated when such secretory granules were incubated with ¹²⁵I‐calmodulin.