The purpose of this study was to investigate the concentrations of Leukotriene B4 in relation to the clinical symptom of pulpitis in human dental pulp. Pulps obtained from 3 groups of teeth: normal uniflamed teeth(N=22), asymptomatic teeth with deep caries or large restorations(N = 21) and symptomatic teeth with the clinical diagnosis of irreversible pulpitis(N = 15). Pulps were dissected from normal un inflamed teeth and extirpated from asymptomatic and symptomatic teeth during routine endodontic treatment and stored in liquid nitrogen ($-70^{circ}C$). The levels of Leukotriene B4 in individual or pooled pulps were measured by radioimmunoassay and the mean levels of each group were compared statistically(Kruskall-Wallis oneway ANOVA test). The results were as followings : 1. In normal pulp, low levels of Leukotriene B4 were measured. 2. In pulps from asymptomatic and symptomatic teeth had significantly higher levels of Leukotriene B4 than normal pulps(p<0.01). 3. The levels of Leukotriene B4 in pulps from symptomatic teeth were significantly higher than those of pulps from asymptomatic teeth(p<0.01). These results suggest that Leukotriene B4 play a cretain role in inflammatory process of dental pulp and have a relationship with clinical symptoms of pulpitis.