EDINBURGH bookseller James Thin recently celebrated its 150th anniversary with a gathering that honoured six generations of the famous family firm.

Established by James Thin in April 1848 the bookshop in

Infirmary Street was run as a one-man operation until Thin was joined by his son in 1880.

During his tenure James Thin bought several of the adjoining shops and flats in the tenement. The headquarters now encompass almost the entire tenement and Thin boasts 35 branches in the UK, 17 in Scotland, with 650 staff and stocks of 85,000 different titles.

It became a limited company in the 1970s and is believed to be one of Scotland's oldest family firms.

When chairman and managing direction Ainslie Thin joined as a partner 41 years ago, Thin consisted of the original shop and 30 staff.

''Our turnover has grown from under #10m to #35m in the last six years,'' he said. ''We've twice won the Price Waterhouse middle-market award for the fastest-growing independent company in the UK. We've been in the top 100 for two years.''

Ainslie Thin was a fourth generation to take the helm. His father, a chemical analyst, was one of few Thins not to join the business. Ainslie, a chemistry graduate, was ready to join ICI until last-minute doubts changed his mind.

Eldest sons succeeded in the second and third generation and Ainslie's three children have, over the last eight years, become influential members of the team.

Daughter Jackie, a qualified chartered accountant, is finance director. Hilary is regional director for the North and son Jamie added an MSc in computing to a teaching qualification before joining in 1994.

The son's credentials make him an ideal candidate to manage book selection, stock control and computer information systems. The South Bridge shop began using a computerised system for ordering and stock control in the mid 1960s - the first such use in a UK bookshop.

A system was subsequently developed by Ainslie Thin which enabled the company to operate economic stock control within 26 of the company's bookshops.

Only now is this being replaced by a superior system designed to link with publishers.

Half of Thin's business focuses on educational texts. The founder's interest in religion manifested itself in a collection of 2500 international hymn books.

After his death, aged 92 in 1915, these were donated to New College Library. Thin's business brought him into contact with literary luminaries such as Thomas Carlyle and Robert Louis

Stevenson.

Fifteen of today's leading

Scottish authors, including Dorothy Dunnett, Nigel Tranter and Ian Rankin, joined in the company's recent anniversary celebrations. Ainslie Thin has high hopes that grand-daughter Holly will one day join the business.

But family recruitment, he stresses, has to be finely balanced. ''It mustn't be rammed down people's throats. They may not be the right people anyway.''

Whatever the future holds, the Thin family intends to uphold the founder's belief that bookselling ''is a calling of a very high order . . . a civilising force''.

The company has survived an arson attack. It has witnessed massive growth in science fiction, feminist writing and publishing in general with 100,000 new titles appearing annually in the UK.

Chairman for a decade, Ainslie Thin believes the right qualities must be brought to the job, there must be an interest in books, of course, friendly and knowledgeable dealings with the public and a capacity for hard work.

''And, as a family member, it's always useful to set a good example by working harder than everyone else,'' he reflected.