In contrast with the transient pre‐replicative increase in calmodulin (CaM) level observed in proliferative activated cells, postnatal development of rat testis was paralleled by 3 specific rises in CaM. The first one occurred between 5 and 10 days, coincident with the appearance and proliferation start of spermatogonia and Sertoli cells. Meiosis accomplishment and spermatid differentiation were paralleled by 2 additional rises, at 24 and 32 days, respectively. The plateau phase of testis growth was coincident with the appearance of maturating spermatids and spermatozoa in the germinal epithelium, and with a decrease in CaM content. Testicular DNA:g wet tissue ratio reached the highest level in 15‐day‐old rats and gradually decreased up to 35 days, when a constant level was reached. A similar level of Ca2+‐CaMBPs was observed in 5‐ and 20‐day‐old rat testis. Although all subcellular fractions showed the ability to bind CaM in a Ca2+‐dependent manner, CaM was mainly recovered in the nuclear and soluble fractions of adult and immature rat testis. Several Ca2+‐CaMBPs with an apparent Mr of 82, 75, 64, 19, and 14 kD were purified by affinity chromatography from pachytene primary spermatocyte nuclear matrix. Ca2+‐CaMBPs showing an Mr of 120, 78, 72, and 66 kD were also purified from the supernatant obtained after DNA and RNA hydrolysis of meiotic nuclei. Major cytosolic Ca2+‐CaMBPs of primary spermatocytes showed an Mr of 120, 84, 44, and 39 kD. The functions that these Ca2+‐CaMBPs might have during the first meiotic prophase is discussed. Mol. Reprod. Dev. 48:127–136, 1997. © 1997 Wiley‐Liss, Inc.