OBJECTIVE: Since 1999,the Ministry of Public Health (MOPH),Thailand,has developed website to inform reference drug price to public health service institutions. The objectives of this study were to analyze the available reference drug price data and compare the price based on Weighted Average Price (WAP) and Drug Price Discrepancy Index (DPDI).METHODS:Drug price data in 2001 were used for the analyses. The 62 drugs from a provincial collective drug purchasing database were selected based on the their high expenditure and the same 62 drugs were also selected from an individual purchasing database for studying their purchasing prices. The WAP and DPDI of individual drugs were calculated. The WAP was calculated from every unit price and volume purchased divided by total amount of drug purchased. Drug Price Discrepancy Index (DPDI) was the ratio of the individual unit price of each collective purchasing group and the WAP. To determine high unit price of purchased drug for individual collective purchasing group, the acceptable DPDI was set up to be no greater than 1.2. The WAP and DPDI of each drug were compared within the collective or individual purchasing group. RESULTS: Of the drug purchased by collective purchasing at provincial level, 15 (24%) drugs had a high purchasing price and of the drug purchased by individual purchasing, 20 (32%) drugs had high a purchasing price. The WAP and DPDI parameter provided the group of target drugs to be monitored to prevent highly purchased drug prices.CONCLUSIONS: The WAP might be used to assist hospital in drug procurement to improve the efficient use of the pharmacy budget. Other affiliating factors including quality of drug should also be considered in actual purchasing. It is anticipated that the DPDI will enable the collective purchasing network and MOPH to be aware of high unit prices of drugs purchased around the country.