The concentration of thiocyanate and ionizable iodine was determined with saliva samples from two test groups, smokers (N = 27) and nonsmokers (N = 92). The contents of both ions were also compared as to sex and the amount of cigarettes smoked. The concentrations of the ions studied were dependent on each other-the less iodine, the more thiocyanate in the samples. Females had significantly more iodine and less thiocyanate concentrations than males. Smoking had an increasing effect on the concentration of thiocyanate and a decreasing effect on the content of ionizable iodine in the saliva of the volunteers. The lower amount of iodine ions in the saliva of smokers may restrict the nonthyroidal metabolism of the thyroid hormone in humans.