Carl Lennertz resigned March 19 as associate publisher and director of marketing and advertising for Little, Brown. Lennertz joined LB last February, after having spent 18 years with Random House. At press time, no one had been named to replace Lennertz; he reported to Sarah Crichton, publisher of LB. Lennertz told PW that he is "a marketing guy" and plans "on staying in the book business."