One of the original cast members of the long-running
On Tuesday, Helgenberger wrote, "Very excited to see my pals @CSI_CBS for the 300th."
Helgenberger was originally teamed with William Peterson when the show began in 2000 and stayed on through the arrival of two other leading men: Laurence Fishburne and Ted Danson. She left the show midway through its 12th season.
Her character, Catherine Willows, a crime scene investigator supervisor and forensic scientist, accepted a job with the
"You haven't seen the last of me," she told the Associated Press in 2012.
The new season of "CSI" begins Sept. 25.