Abstract: AIM: To investigate the effect of human parathyroid hormone(1-34) ［hPTH(1-34)］ on alkaline phosphatase(ALP) activity of osteoblastic cells. METHODS: Osteoblastic cells were isolated from newborn rat calvaria through trypsin digestion. Quality of the cells was assessed by special ALP histochemistry. The activity of ALP was measured by p-nitrophenyl sodium phosphate assay. The expression of ALP mRNA was detected by RT-PCR. RESULTS: Cellular ALP activity was increased obviously while osteoblastic cells were incubated with 10^-8 mol．L^-1 hPTH(1-34) for the first 12 h of each 48 h incubation cycle and repeated the cycle for 8 times. Cellular ALP activity showed no obvious changes at continuous exposure to hPTH(1-34) compared with control group. Expression of ALP mRNA was increased greatest while osteoblastic cells were incubated with 10^-8 mol．L^-1 hPTH(1-34) for the first 12 h of each 48 h incubation cycle and repeated the cycle for 8 times. CONCLUSION: hPTH(1-34) has diverse effects on osteoblastics ALP activity depending on the exposure time and its concentration in vitro, cellular ALP activity increases under intermittent exposure to hPTH(1-34).