Another four people have apparently killed themselves using a home-made gas, the latest in a wave of similar suicides sweeping the country.
Victims use bath cleaner and other household chemicals to create a mixture that gives off deadly fumes.
At least 50 people killed themselves with it last month.
The latest cases were found dead together in a car.
A police spokesman said the bodies of three men and a woman – all in their 20s and 30s – were found by a patrolling officer in Takashima, western Japan.
Police found bottles of bath detergent and other chemicals.