Developmental competence of oocytes is progressively obtained, both as females reach puberty and as follicular diameter increases. The poor quality of oocytes, and the subsequent embryos derived from them, in prepubertal females and from small follicle sizes suggests that essential processes during cytoplasmic maturation of the oocyte have not been fulfilled. The objective of this experiment was to identify differentially expressed genes in oocytes derived from gilts or sows and from large or small follicle sizes that correlate with developmental competence. Oocytes were collected from 2–6 mm (sows and gilts) and 8–14 mm follicles (sows) and matured in vitro for 42–44 hrs in defined TCM199 supplemented with 0.5 mM cysteamine, 0.5 mM citric acid, 100 ng/ml epidermal growth factor, 0.05% ITS (v/v), 0.01% recombumin (v/v), 0.1 U/ml porcine LH and FSH and 2 mg/ml fetuin. Mature oocytes were identified by the presence of the first polar body in a Hepes buffered medium supplemented with 5% sucrose, lysed in pools of 150 and the poly A+ RNA extracted. Samples were processed through two cycles of linear amplification and hybridized to Affymetrix Porcine Genome Arrays. Microarray data was sorted and filtered by gene and by treatment to remove genes that were classified as having two absent calls per treatment. The data was then normalized and analyzed using a one-way analysis of variance. Level of significance was calculated using the Benjamini and Hochberg False Discovery Rate (FDR) and Bonferroni correction of α < 0.0167. A total of 11,600 genes were identified as present in the sow 2–6 mm and sow 8–14 mm treatment groups, with over 3500 genes (30.5%) being differentially expressed. Genes differentially expressed in oocytes derived from sow 2–6 and 8–14 mm follicles include genes involved in regulation of oxidative stress (glutathione S-transferase and peroxiredoxin 5), growth factors (growth differentiation factor 9 and insulin-like growth factor 2), and metabolism (pyruvate caboxylase). Over 12,200 genes were present in the sow 2–6 mm and gilt 2–6 mm treatment groups but only 1500 genes (12.9%) were differentially expressed. Oocytes derived from sow 2–6 mm and gilt 2–6 mm follicles differentially expressed growth factors (bone morphogenic protein 15), genes involved in programmed cell death (anti-apoptotic bcl), regulation of oxidative stress (gluthathione S-transferase and peroxiredoxin 1 and 4), metabolism (phosphoenolpyruvate carboxykinase 2) and DNA methyltransferases (Dnmt 1). Gene expression is significantly affected by maternal age as puberty approaches, as well as follicle size, and may be the basis for differences observed in developmental competence of porcine oocytes. (poster)