BAC K G R O U N D We hypoth es ized that pleural fluid levels of Vit D might be higher and pleural fluid levels of parath o rm one (PTH) might be lower in patients with tub e rcul ous pleural effusion (TPE) than those in pat ients with non-tub e rc ul ous p l e ural eff us ion. We also hypoth es ized that the abov e - mentioned hypoth esis is valid for the serum val ues. M ET H O D S Twenty TPE patients, 17 non-TPE patients and 20 healthy controls were enrolled into the study. Serum and pleural fluid Vit D, PTH, calcium (Ca), magnesium (Mg) and phosphorus (P) levels were measured in each group. R E S U LT S Mean serum Vit D level (117.8±47.6 ng/ml) in TPE patients was higher than that (71.8±31.2 ng/ml) in non-TPE patients (p<0.05) and that (41.2±13.0 ng/ml) in control group. Mean pleural fluid Vit D level (38.2±16.3 ng/ml) in TPE patients was higher than that (14.1±11.1 ng/ml) in non-TPE patients (p<0.05). Mean serum PTH level (27.3±13.3 ng/L) was lower in TPE patients than that (64.6±24.7 ng/L) in non-TPE patients (p<0.05). Mean pleural fluid PTH level (6.7±3.8 ng/L) was lower in TPE patients than that (14.7±8.5 ng/L) in non-TPE patients (p<0.05). CO N C L U S I O N S In conclusion, this study suggests that there might be a significant difference in Ca metabolism among the patients with TPE, the patients with non-TPE, and controls.