We aimed to investigate the effect of smoking on the osmotic pressure [OP] of human dental pulp tissue. Sixty male dental patients [smokers and nonsmokers] scheduled for root canal treatment for prosthodontics were included in the study. Fifteen patients [1 premolar tooth/patient] were allocated to each of the following groups according to their smoking habits, i. e. group 1: <10 cigarettes/day, group 2: 11-20 cigarettes/day, group 3: >20 cigarettes/day and group 4: nonsmoking controls. Apical pulp tissues were removed via coronal access. Pulp tissue supernatants were obtained to measure the pulpal OP by means of a semimicro digital osmometer. One-way analysis of variance and the post hoc Duncan test were used to analyze the differences in OP between groups. Regression analysis was used to determine the relationship between the number of cigarettes smoked daily and the pulpal OP. The mean [ +/- SD] OP value decreased as cigarette consumption increased: group 4 [268.00 +/- 10.09 mosm/kg] > group 1 [259.20 +/- 7.16 mosm/kg] > group 2 [248.90 +/- 2.23 mosm/kg] > group 3 [239.90 +/- 7.40 mosm/kg] . The OP differed significantly between groups [p < 0.01] , and a significant negative correlation was found between cigarette consumption and pulpal OP [r = -0.809, p < 0.01] . In this study, the OP decreased as the number of cigarettes smoked increased. In clinical examination, there may be mis-diagnosis of pulpal conditions in smokers [even in healthy pulp tissue] due to the effect of altered OP on pulpal tissue reactions.