Yellow spines in the loud trademark color of Let's Go stand out from the travel shelf at Barnes and Nobles, but Lonely Planet guidebooks, which come in all colors, are taking up more and more shelf space. And shelf space, a common industry measurement of publishing success, is a crucial area where Let's Go can't afford to cede ground to a relative newcomer.

In response, St. Martin's Press-the publisher of the Harvard Student Agencies' Let's Go series-is launching new marketing measures, targeting young travelers, who once formed the backbone of the Let's Go readership.

Representatives of St Martin's press say rising Lonely Planet sales could pose a real threat to the Let's Go empire.

Still, since the payment to students who write and edit the guidebooks does not depend on sales, the offices of Let's Go remain largely free from market concerns.

And St. Martin's Press recently renewed the Let's Go contract for another five years .

A CHANGING MARKET

According to a marketing representative at St. Martin's the travel market is shifting as a result of more guidebook titles and more electronic content and specialized itineraries.

"There are a couple of trends that are eroding sales: the Internet and more competition. Lonely Planet was not really a player until the last few years when they decided to attack the European market," says Esti M. Iturralde `00 of St. Martin's Press. Iturralde was a former Let's Go managing editor.