The health effects of chronic exposure to cyanide, with specialemphasis on the thyroid, was studied in 56 workers exposed to cyanide incase hardening and electroplating. Hydrogen cyanide was measured in airof workplace environment. Serum thiocyanate was measured in workersin addition to serum thyroid hormones (T3, T4, TSH). They werecompared with a control group not exposed to cyanide. The serumthiocyanate levels showed high statistically significant levels in exposedworkers compared to the control. Serum TSH showed a statisticallysignificant positive correlation with serum thiocyante in the exposedworkers.