The number of workers testing positive for marijuana use is on the rise, according to a new report from the state's leading workforce drug-testing company.

Diagnostic Laboratory Services reported yesterday that positive test results for THC, the main active chemical in marijuana, rose 8 percent in the second quarter from the same period last year, and 69 percent from the second quarter of 2007.

DLS also said 2.7 percent of those who took pre-employment drug tests during the April-June period tested positive for marijuana. That was up from 1.6 percent in the second quarter of 2008, and was the largest percentage since the company began keeping records in 2004. DLS said its quarterly sample size typically includes between 5,000 to 10,000 drug tests.

Positive tests for amphetamines, cocaine and opiates were roughly the same over the past year, said Carl Linden, the lab's scientific director of toxicology.

Linden said one reason for the higher marijuana use could be that illegal drug users are opting for less expensive drugs because of the economic downturn. However, he emphasized that there was no hard evidence to confirm that.

Michelle Yu, spokeswoman for the Honolulu Police Department, said the numbers don't measure actual marijuana use, and the department avoids drawing any kind of relationship between drug-testing statistics and drug popularity.