Aerosol penetration into the maxillary sinus after nebulization has not fully investigated yet. We have evaluated the patency of the natural ostium of ten normal adults(twenty sinuses) and five patients(nine sinuses) following sinus operation by Caldwell-Luc's method. Phytate aerosols labeled with Tc^99m were inhaled into the noses and gamma camera computer system was used to measure the dose of radioaerosol deposit in the maxillary sinuses and then compared with that measured at the respective frontal portions. The results are follows : 1) In normal adults, the average RI count ratio of maxillary sinus to frontal sinus was about 6.1. 2) In the postoperative patients, the average ratio was only about 1.6.