Nick Stahl is back in jail after getting busted for drugs early this morning ... TMZ has learned.
LAPD tells us the "Terminator 3" star was arrested around 5 AM when police found him in a Hollywood motel with three other people ... they were all allegedly using meth.
Stahl was taken into custody -- along with the other individuals.
We're told police actually went to the motel to conduct a parole compliance check on one of the people Stahl was hanging with this morning.
Wrong place, wrong time for Stahl ... who's battled drug addiction for years.
Just yesterday, Nick told us he was happy he was placed on a 5150 hold earlier this month -- because it helped straighten him out.