Cigarettes made up almost half of the objects accidentally swallowed by babies in fiscal 1997, according to a Health and Welfare Ministry report.
Cigarettes have headed the list every year since the ministry began the survey in 1979 to monitor accidents related to household items.
Of the 871 tallied cases in which infants accidentally ingested objects, 402 involved cigarettes, constituting 46 percent of the cases. Little improvement was noted from the previous year's 48 percent.
In most of the cases, babies put cigarettes or cigarette butts into their mouths, but there were also incidents where babies drank water from aluminum cans used as ashtrays.
Roughly three-quarters of all cases involved infants between 6 months and 1 year old, and objects accidentally ingested included medicine, toys and batteries, according to the survey.
"We want people to be more aware that almost all household objects can potentially be swallowed by babies," a ministry official said, calling for increased vigilance on the part of guardians.
The survey compiled reports from the pediatric wards of eight major hospitals, including Keio University Hospital.
Button batteries made up 31 of the 34 cases involving batteries. These small, round batteries are increasingly used in children's toys and have caused anxiety because they can potentially stick to the inner walls of the stomach or intestine and open holes in the organs.
Toys need to be designed so that battery lids do not open during play, ministry officials said.