Objective: To evaluate the effects of tumor necrosis factor-alpha (TNF-α) on porcine oocyte maturation, spindle dynamics, and chromosome alignment. Design: Controlled, prospective study. Setting: University hospital and IVF research laboratory. Animal(s): Ovaries collected from slaughtered prepubertal gilts. Main Outcome Measure(s): Oocyte maturation rate and cytoskeleton distribution. Materials and Method(s): Immature porcine oocytes (GV) were exposed to TNF-α at a concentration of 0 (as a control), 1, 5, 10, 100, 200, or 600 ng/mL in M199 medium. Oocytes were cultured for 24 hours to the pre-MI stage or 44 hours to the MII stage. After in vitro maturation for 44 hours, the rates of GV oocytes reaching MII stage were assessed, and MII oocytes were fixed for further examination of the cytoskeleton and the chromosomal distribution. Result(s): The TNF-α concentration at 5 ng/mL decreased the porcine oocyte maturation rate compared with the control after culture for 44 hours, whereas exposure to 10 or 100 ng/mL TNF-α resulted in a significant increase in the frequency of defective spindles or abnormal microfilament distribution. Exposed to 200 ng/mL, TNF-α caused a significantly higher abnormality rate of chromosome alignment when compared with the controls. Conclusion(s): Exposure of porcine oocytes to an elevated TNF-α concentration clearly caused a reduction in their maturation from GV stage to MII stage and increased the proportion of oocytes with abnormal chromosome alignment and cytoskeleton structure. © 2010 American Society for Reproductive Medicine.