PURPOSE To estimate the daily cost of various ophthalmic solutions used in Japan for treating allergic conjunctivitis, including nine anti-allergic drugs and six anti-inflammatory drugs. METHODS The drops contained in one bottle of each solution were counted. The cost per drop was calculated by dividing the government-controlled standard prices by the total number of drops in one bottle, and the daily cost of therapy was calculated by multiplying the cost per drop by the number of drops to be given per day. RESULTS The total number of drops of the anti-allergic drugs in a bottle ranged from 108 to 169 and that of the anti-inflammatory drugs from 100 to 145. The information in the package insert for these solutions recommends application 2-4 times daily. The price of the antiallergic drugs studied ranged from $6.35 to $8.38 and that of the anti-inflammatory drugs studied from $2.02 to $5.20. The daily cost of the anti-allergic drugs studied varied considerably, from $0.26 to $0.57; for the anti-inflammatory drugs the range was from $0.12 to $0.20. Variations in the total number of drops per bottle and in the recommended dosage affect the daily cost of ophthalmic solutions. CONCLUSIONS At current prices, the volume of a drop and the dosage had a greater effect on the daily cost than the price of a bottle. Daily cost data may be helpful in selecting ophthalmic products for treating allergic conjunctivitis in settings where the prices of a given drug are relatively uniform.