Melatonin is the main product of the pineal gland, and trace metals play a critical role in growth and development. The purpose of this study was to assess the serum zinc (Zn) and magnesium (Mg) levels in pinealectomized chicks and their possible interactions with the development of spinal deformity. Chicks were divided into two equal groups: unoperated controls (group M) and pinealectomized chicks (group N). Pinealectomies were performed at the age of 3 d. After 8 wk, serum Zn and Mg levels of 10 animals from each group were measured by spectrophotometric assay. The results of analyses were compared using the Mann-Whitney U-test. The correlation between serum Zn and Mg levels were assessed by Spearman's correlation. In this study, it was obvious that the serum Zn levels in group N were significantly lower than those in group M (2.8 +/- 0.10 vs 4.2 +/- 0.14 ppm; p < 0.0005). In contrast, Mg levels in group N was high compared with the values in group M, although there was no significant difference (17.8 +/- 0.69 vs 15.7 +/- 0.85 ppm; p > 0.05). In pinealectomized animals, serum Zn levels declined significantly while serum Mg levels increased, albeit insignificantly. Thus, there was a moderately positive but not statistically significant correlation between Mg and Zn levels in unoperated controls (r = 0. 273, p > 0.05), whereas there was a negative but not statistically significant correlation between Zn and Mg levels in pinealectomized chicks (r = -0.115, p > 0.05). In addition, the serum Mg to serum Zn ratio was significantly higher in group N than in the group M control (6. 39 +/- 0.32 vs 3.75 +/- 0.22, respectively; p < 0.001). From the results of the current study, it is clear that surgical pinealectomy in newly hatched Hybro Broiler chicks has a significant effect on serum Zn level. However, the serum Mg did not change significantly. Because serum Mg is not a good indicator of Mg status in chicks, it is speculated that other tissues, such as muscle or spine, might productively be explored as a more sensitive Mg biomarker for this model. The present study provides experimental evidence that serum trace metal levels might be affected in pinealectomized animals because of the lack of its main neurohormone melatonin.