Technetium-99m-hexamethylpropyleneamine oxime $(^{99m}Tc-HM-PAO)$ is a neutral-lipophilic chelate which is used for scanning cerebral blood flow. The labeling efficiencies of $^{99m}Tc-HM-PAO$ is known to be sensitive to the amount of pertechnetate added and the quality of the pertechnetate. Because of these factors, the manufacture recommends that HM-PAO kits be reconstituted with a maximum of 30 mCi pertechnetate which was eluted <4 hr earlier from a generator which had been eluted < 24 hr previously. So we measured the labelling efficiencies and the decomposition rate constant according to the amount of pertechnetate added, the volume of pertechnette added, and generator in-growth time. We used the 3-system chromatographic methods (paper & ITLC-SG chromatography) which analyzed the labelling efficiencies of the $^{99m}Tc-HM-PAO$. There was no significant difference in labelling efficiencies between variable pertechnetate acitvities added. ($39.9{pm}4.9;mCi:;87.8{pm}5.1;(%)$, $60.8{pm}5.0;mCi:;90.7{pm}2.2;(%)$, $79.0{pm}6.0;mCi:;86.8{pm}3.9;(%)$, $106.6{pm}11.6;mCi:;87.7{pm}1.2;(%)$, p>0.05) No significant difference in labelling efficiencies were found between pertechnetate of 4ml and 5ml. (4ml : $89.1{pm}3.2(%)$, 5ml: $87.3{pm}4.0(%)$, p>0.05). There was no difference between 1-6 and 10-48 hr of generator in-growth time. (1-6 hr: $87.8{pm}4.0(%)$, 10-48 hr: $89.6{pm}1.6(%)$, p>0.05) The mean value of decomposition rate constant was $0.196{pm}0.097;(hr^{-1})$, and there were no difference according to the amount of pertecnetate added and the volume of pertecnetate added, ($39.9{pm}4.9;mCi:;0.208{pm}0.059;(hr^{-1})$, $60.8{pm}5.0;mCi:;0.191{pm}0.100;(hr^{-1})$ $79.0{pm}6.0;mCi:;0.192{pm}0.118;(hr^{-1})$, $106.6{pm}11.6;mCi:;0.212{pm}0.030;(hr^{-1})$, p>0.05, 4 ml: $0.200{pm}0.074;(hr^{-1})$, Sml: $0.193{pm}0.115;(hr^{-1})$, p>0.05). In the case of using the first eluate, the labelling efficiency of $^{99m}Tc-HM-PAO$ W3S 82.1%. These data suggest that there were no significant alteration in labelling efficiency of $^{99m}Tc-HM-PAO$ according to the considerable range of pertechnetate activities and volume added, and generator in-growth time. Also, it was shown that one vial of HM-PAO kit supplied the $^{99m}Tc-HM-PAO$ which was used for 3-4 patients.