Bristol's two NHS health care trusts have merged to become one operation from Sunday.
The Bristol Primary Care Trust has taken over from Bristol South and West and Bristol North PCT.
Managers said the trust would serve a population of about 400,000 and had an annual budget of £570m.
In Gloucestershire, a county-wide PCT replaced three existing trusts in Cotswold & Vale, West Gloucestershire and Cheltenham and Tewkesbury.
Jan Stubbings, chief executive of Gloucestershire PCT, said: "We have a significant challenge to protect the range of services provided, provide more services closer to the patients home and at the same time live within our means financially."
Deborah Evans, formerly the chief executive of Bristol South and West PCT, said: "We share the same boundaries as Bristol City Council and together we will build on providing an even better seamless service for local people."
The mergers are part of a shake-up of local health bodies which will see 303 primary care trusts in England joined to make 152 larger trusts.