The effects of BHSH on L-DOPA-induced increase in dopamine content in PC12 cells were investigated. L-DOPA treatment at $20;or;50;{mu}M$ increased dopamine content after both 24 and 48 h of incubation in PC12 cells. However, the co-treatments of BHSH $(10-50;{mu}M)$ with L-DOPA $(20;or;50;{mu}M)$ significantly inhibited the increase of dopamine content induced by L-DOPA. BHSH treatment at $10-50;{mu}M$ significantly inhibited basal aromatic L-amino acid decarboxylase (AADC) activity in a concentration-dependent manner at 15 min, and then AADC activity was rapidly recovered to the control level at about 2 h. These results indicate that the inhibition of AADC activity by BHSH was, in part, contributed to the early-stage decrease of dopamine content induced by LDOPA in PC12 cells. Taken together, it is proposed that the short-term inhibition of dopamine biosynthesis by BHSH was mediated by the regulation of tyrosine hydroxylace (TH).