[JKnight]

The issue in the interim period will be that you can't contribute pre-tax money from your pay. I'm a little surprised they are handling the transition in a way that doesn't have you participating in the acquiring firm's plan prior to stopping contributions into the existing. Trey's point about funding a Roth during that period is valid, but those will have to be after-tax dollars. I'd ask your firm's HR group for more info about your options during this period. If they don't provide a mechanism for pre-tax contributions, you don't really have an option to continue that.