The objective of this study was to investigate the effects of iodine deficiency on pulmonary xenobiotic metabolizing enzyme systems in rats. Three-week old male Wistar rats were fed for seven weeks. Iodine deficiency was produced by sodium perchlorate containing drinking water. The total microsomal cytochrome P450 (CYP450) and cytochrome b5 (CYP b5) levels; activities of microsomal NADPH-cytochrome P450 reductase (P450R), microsomal aniline hydroxylase (CYP2E1), microsomal ethoxyresorufin O-deethylase (EROD), microsomal pentoxyresorufin O-depenthylase (PROD) and cytosolic glutathione S-transferase (GST) were determined. Significant decreases in the level of total CYP450; in the activities of P450R, CYP2E1 and GST; increases in the level of CYP b5 and the activities of EROD and PROD were observed. Overall results of this study have indicated the occurrence of significant alterations in pulmonary xenobiotic metabolism in iodine deficient pubertal rats.