PHOENIX - Arizona DEA agents work hundreds of drug cases a year. Agents often find pounds and pounds of marijuana and cocaine.

Some of the clandestine labs they bust are used for making meth or Spice. Rarely are agents surprised by what they find, but a recent bust uncovered something they’ve never seen before.

“It was like, 'oh wow,'” said DEA Special Agent Doug Coleman.

During a recent investigation, agents uncovered what is believed to be the nation’s first Spice lab using Fentanyl.

“We found many pounds of the Spice product and when you consider it is usually sold in gram quantities and Fentanyl itself is used in microgram quantities, you are talking about hundreds of thousands of doses could have gone out to street,” Coleman said.

The Spice was laced with Fentanyl -- the dealers used a cement mixer to combine the two drugs.

“[Fentanyl] is so powerful it’s given in micro-gram quantities,” said Coleman.

Four people were arrested and DEA agents say more arrests are coming.

“This is a high-priority case," said Coleman. "Again, this is a trend we have never seen before."

The concern, along with catching the dealers and their distributors, is getting the word out to potential Spice users that what they may be smoking could be laced with Fentanyl.

“A very small amount of this can cause overdose deaths,” Coleman said.

Spice is illegal and can be deadly, but when mixed with Fentanyl the risk is increased.

“You could get a leaf with 50 micrograms on it while another leaf could have two on it. If you get the one with 50, you’re a goner,” said Coleman.

Agents couldn’t talk much about the specifics of this case because it is ongoing. 12 News has learned the homemade lab was inside a house in north Phoenix. The suspects are apparently all Arizona residents between the ages of 30 and 40 years old.

In the past 18 months, Arizona DEA agents have seized more than 35 pounds of Fentanyl, which equates to more than 7.5 million doses.

It is unclear how long this Spice lab was in operation, which means agents have no idea how much -- if any -- Fentanyl-laced Spice is out on the street.

“I say it’s not just a chance, but probability there is Spice on the streets of Arizona laced with Fentanyl,” said Coleman.