Series high (again!) for 'Dexter'

"Dexter" is becoming Showtime's "True Blood."

Like HBO's dark hit this summer, "Dexter" keeps growing with nearly each episode, hitting another series high Sunday night -- 1.9 million viewers for its first airing.

The series has gained more than 600,000 viewers over the past three weeks. Compare that to Sunday's "Mad Men" (which matched its season average of 1.8 million) and AMC has roughly quadruple the potential audience over Showtime.