Hyperthyroidism may influence sensitivity to insulin. The aim of study was to assess insulin resistance in hyperthyroid patients in correlation with the plasma free thyroxine (FT4) and thyreotropin (TSH) concentrations.The study group consisted of 15 hyperthyroid patients (11 females, 4 males, mean age 50, 6 +/- 12, 36 yrs.). The controls were 17 healthy individuals (6 females, 11 males, mean age 55, 12 +/- 14, 17 yrs.). In the study group the mean FT4 was 33.1 +/- 20.1 pmol/l, TSH 0.034 +/- 0.066 pmol/l, glucose 5.00 +/- 0.56 mmol/l, insulin 7.19 +/- 3.59 microU/mL. In the controls respectively: 16.2 +/- 1.8 pmol/l, 1.24 +/- 1.07 pmol/l, 5.04 +/- 0.62 mmol/l, 7.24 +/- 4.06 microU/mL. Insulin resistance was calculated with HOMA-IR model, and the results were in the study group: mean 1.63 +/- 0.85, range from 0.46 to 3.67, median 1.38; in the controls respectively: 1.69 +/- 1.08, range from 0.36 to 4.47, median 1.42.Insulin resistance did not differ significantly between the groups (p=0.8860). FT4 and TSH did not influence insulin resistance in either group, the correlations were insignificant: for FT4 and for TSH p=0.5100 and p=0.5601 in the study group, and p=0.172 and p=0.4509 in the controls, respectively.Hyperthyroidism did not influence insulin resistance assessed with HOMA-IR model in vivo.