Police say a 22-year-old man was stabbed at the Crescent Street J train subway station in Cypress Hills.
Officials suspended northbound service for about an hour as police investigated.
Police sources say it happened around 4:20 p.m., during the commuter rush.
The victim and another person became involved in an altercation that escalated into violence.
The victim was taken to a hospital and is expected to be OK.
Straphangers say the seemingly growing number of knife attacks on the city's subways is disturbing.
A little more than a month ago, a similar incident occurred at the No. 3 train platform on Pennsylvania Avenue. And in January, a man with a machete slashed another woman on the No. 3 train.
Anyone with information on the latest incident is asked to call Crime Stoppers at 1-800-577-TIPS.