''Bedrock bathing'' enabling bathers to sweat on warmed slates is rapidly becoming popular in Hokkaido, chiefly in Sapporo where at least 130 such bathhouses are concentrated.
     It is especially popular among women. ''Unlike in a sauna, you can sweat without feeling pain, and it is good for your figure and diet,'' said a woman. Such bathhouses are said to number about 300 in the country.
     A bathhouse owner in Hokkaido said, ''We would like to make it a noted thing from Hokkaido, following a Mongolian mutton barbeque and a soup curry dish.''
     Bathers put towels on slates made of black silica and other minerals, which are warmed to 45 C with hot-water pipes, and lie down on them with indoor clothing on.
     The bathhouse temperature is kept at about 40 C with humidity of 50-70 percent. After 10 to 20 minutes on the slates, bathers take a break and drink water, which is generally repeated three times.
     Tetsuya Sakurai, who was so attracted to bedrock bathing that he quit his company two years ago to enter the business, now operates two bathhouses in Sapporo, including one named Sakura in Sapporo's Chuo Ward catering exclusively for women. ''You can sweat naturally with far-infrared rays from warmed stones, improving the circulation of your blood,'' he said.
     A 32-year-old female assistant nurse, who goes to the bathhouse once or twice a month, said, ''I feel good with much sweat, and it is also good for my skin. About 30 percent of my colleagues go there.''
     An official of the Sapporo municipal government said the registration of such bathhouses began to increase sharply last year.
     Bedrock bathing is said to have originated in the northeastern part of the main island of Honshu.
     A bathhouse owner who began such bathing in the city of Date for the first time in Hokkaido said, ''I learned about bedrock bathing at an inn in the city of Kesennuma in Miyagi Prefecture.''
     The owner of the inn, who inherited its management, said he created a bedrock bathhouse with a health method of warming bodies on rocks warmed by terrestrial heat at Tamagawa Hot Spring in Akita Prefecture as a hint.
     Many bedrock bathhouses in Hokkaido are chiefly for women, but there are some where men can also enjoy bathing. Recently, the number of such bathhouses creating beauty-treatment and therapeutic clinics is increasing to aim at a multiplier effect.
     Industry sources said the number is increasing because investments in bedrocks bathhouses are relatively small. They can be opened by remodeling vacant rooms in buildings, they said.
     Hayashi Construction Industry Co., a Sapporo-based company in Sapporo building bedrock bathhouses, said, ''Although Hokkaido is leading their popularity, we would like to spread them across the country. There are also orders from facilities for the aged.''
     But the sources said some bathhouse operators are advertising that bedrock bathing is effective in treating cancer, giving rise to concern about misleading representation.
     An industry executive said, ''In order not to end bedrock bathing as a temporary boom, the whole industry will have to pay attention to the representation of its effects.''
==Kyodo