BOCA RATON, Fla. -- A pair of masked robbers who struck two pharmacies in unincorporated Palm Beach County near Boca Raton might be the same men responsible for a recent rash of robberies to other pharmacies throughout South Florida.

At 3:26 a.m. Thursday, two men, one of them armed, entered a Walgreens at 9851 Glades Road. The men ordered the pharmacist behind the counter to open the register, but they left for some reason before any money was taken.

About 30 minutes later, the same men entered a CVS at 10055 Yamato Road and were successful in demanding an undisclosed amount of money from several locations inside the store.

The men were wearing all black, black masks and black gloves. One of the men was wearing a white or gray hat and the other was wearing a black hat.

Their descriptions match a pair of men who appear to be on a pharmacy robbery spree. There have been 16 robberies of CVS or Walgreens pharmacies in Broward and southern Palm Beach counties since May. Thursday's incidents bring the total to 18.

All the robberies have been committed by two men wearing Halloween or ski masks during overnight hours. In most cases, they made the managers open the vault to the safe. In some instances, they have stolen customers' and employees' cell phones.

Authorities said they have increased their patrols of the 24-hour pharmacy stores and management has said they bolstered their surveillance systems, but it hasn't seemed to help.

"Everything's being done that can be done and we do anticipate an arrest" said Carol Hively, a spokeswoman for Walgreens.