The thermoluminescence dosemeter (TLD) was used for measuring radiation dose to family members of thyrotoxicosis and thyroid cancer patients treated with (131)I using CaSO(4):Dy discs. There were 45 family members of thyrotoxicosis patients, who were divided into two groups with 22 in the first and 23 in the second group. Radiation safety instructions were the same for both the groups except in the second group where the patients were advised to use a separate bed at home for the first 3 d of dose administration. An activity ranging from 185 to 500 MBq was administered to these patients. The whole-body dose to family members ranged from 0.4 to 2.4 mSv (mean 1.1 mSv) in the first group and 0-1.9 mSv (mean 0.6 mSv) in the second group. A total of 297 family members of thyroid cancer patients were studied for whole-body dose estimation. An activity ranging from 0.925 to 7.4 GBq was administered to the thyroid cancer patients. The family members were divided into three groups depending upon the mode of transport and facilities available at home to avoid close proximity with the patient. Group A with 25 family members received a dose ranging from 0 to 0.9 mSv (mean 0.4 mSv), group B with 96 family members received a dose ranging from 0 to 8.5 mSv (mean 0.8 mSv) and group C with 176 family members received a dose ranging from 0 to 5.0 mSv (mean 0.8 mSv). The thyroid monitoring was also done in 103 family members who attended the patients in isolation wards for >2 d. Thyroid dose in them ranged from 0 to 2.5 mGy (mean 0.1 mGy).