Reproduction biotechnologies depend on the use of fully meiotically competent oocytes. Growing oocytes without full meiotic competence are an interesting potential source due to their quantity, but the mechanisms regulating the processes of acquisition of meiotic competence have not been clarified to date. Nitric oxide synthase (NOS) and its product, nitric oxide (NO), may possibly play a role. Understanding the precise NO regulatory mechanism is therefore important for the development of in vitro growth methods. The objective of this work was to detect changes in the expression of NOS isoforms and their mRNA expression and changes in the intracellular localization of separate NOS isoforms during the growth period of the porcine oocyte, and also to determine whether these changes are related to the process of meiotic competence acquisition. The results indicate that NOS isoforms may significantly influence the acquisition of meiotic competence in porcine oocytes.