PETALUMA -- Kala Brand Music Co. is more than doubling the size of its Petaluma base of operations as sales expand for the 6-year-old producer of exotic ukuleles and novel bass guitars.

The company leased 24,000 square feet at 1105 Industrial Ave. and relocated at the end of March from less than half that amount of space in three separate offices and as many warehouses.

"We have a lot more product coming in, and we ran out of space," said Rick Carlson, director of sales and marketing. The company currently employs 25.

The company contracts with facilities in various countries to make most of the more than 120 models of ukuleles, which retail for $40 to $600, and UBass short-scale bass guitars. Final testing and quality-control inspections are completed in Petaluma.

The local facility does produce some instruments. Components for the California series UBass are made in Southern California and assembled in Petaluma. And pickup electronics for amplification for some custom ukes are installed locally.

"We probably will expand the custom shop eventually," Mr. Carlson said.

The company release sales figures, but Kala's ukuleles are distributed through about 1,000 dealers in the U.S., Asia, Australia, New Zealand, Europe, Russia, Turkey, Central America and, recently, Brazil.

"Ukuleles have gained popularity worldwide and are not just a novelty," Mr. Carlson said.

Historians trace the history of the ukulele to adaptations of Portuguese instruments brought to the Hawaiian islands in the late 1800s. It had peaks and valleys of popularity, two of which were the 1968 Tiny Tim hit "Tiptoe Through the Tulips" and the 2003 medley of "Somewhere Over the Rainbow" and "It's a Wonderful World" by Hawaiian artist Israel Kamakawiwo'ole.

In the early 1990s Kala co-founder Mike Upton noticed revived popularity of the instrument while living in Hawaii. As the sales representative for instrument maker Hohner in the islands starting in the later part of that decade, he helped launch a line of ukes for the company.

In mid-2005 he went out on his own, starting to set up what became Kala in Petaluma, the hometown of his wife, Wendy. The company name comes from Hawaiian words for forgive, exorcising prayer, money and certain fish.

Drawing on his background as a bass guitar player, Mr. Upton then developed the UBass, which is more than just a bass for small hands. With specially designed polyurethane strings, the instrument has a 21-inch string length scale, compared with more than 30 inches for most conventional basses.

Retailing for $450 to $1,000, the UBass has garnered a number of endorsements from professional musicians, most recently from longtime session player Abe Laboriel and up-and-comer Tal Wilkenfield.

The company also is heavily involved in music education in the U.S. and Canada, building a market by helping to promoting the ukulele as a fun and approachable instrument.

"A lot of music stores are learning that a great way to get customers into the store is by offering lessons, and the uke makes it unintimidating to teach how to strum," Mr. Carlson said.