The percentage of junior high and high school students who smoke dropped sharply in fiscal 2004, apparently due to a decline in adult smokers and expensive cell phone bills, a health ministry research team said Monday.

The team conducted a survey on 103,500 students in about 180 junior high and high schools to find out how many of them smoked once or more during the month the poll was conducted. It is illegal for people under age 20 to smoke.

The team found the percentage of male high school seniors who smoked fell to 21.8 percent from 37 percent in the previous two surveys, in 1996 and 2000. The percentage of female high school seniors dropped from 16 percent to 9.7 percent.

The percentage of male seventh-graders aged 12 and 13 who smoked, which was 6 percent to 8 percent in the previous surveys, was down to 3.2 percent.

The declines can be attributed to the decrease in the rate of adults smoking and the increase in nonsmoking areas in public spaces, said Kenji Hayashi, head of the research team of the Health, Labor and Welfare Ministry and an assistant director at the National Institute of Public Health.

"The number of junior high and high school students who own cell phones is increasing," Hayashi said, "and there is a high chance that phone bills are weighing on the money they spend on cigarettes.

"The monthly allowance students get ranges between 6,000 yen and 7,000 yen," he said. "But more than 80 percent of them own a cell phone, and some studies show that the phone bills they pay amount to 4,000 yen to 6,000 yen. We need to further investigate the correlation between the two."