Police in Somerset investigating a fatal road accident are appealing to other motorists for help.
A passing driver found the 42-year-old man on the A359 at Three Ashes, near Wincanton, at about 0730 GMT.
An Avon and Somerset Police spokesman appealed for anyone using the A359 overnight to contact them.
"Anyone who may have seen a motor bike driving in the area between 11pm on Thursday and 7.30am on Friday is asked to contact police," he said.
No other vehicle is thought to be involved.
The road was closed for four hours while the accident was investigated.