With baby boomers now about one-third of the population, the question of how to mark a 50th birthday is being raised frequently these days. One publishing notable, Random House senior v-p and director of corporate PR Stuart Applebaum, recently marked his 50th in a very special way.

At a private dinner party on September 21 that was thrown by his brother, Irwyn Applebaum, president of Bantam Dell, the newly turned 50-year-old made two surprise announcements. To honor three members of his family who have died, he has established a $100,000 endowment fund to the Queens Borough Public Library to benefit three ongoing programs -- the Mail-A-Book program for homebound people in honor of his mother; a book purchase program in honor of his father; and a LatchKey program for afterschool study for his brother. QBPL was frequented by the Applebaum family, particularly Stuart. He described it as "a place where I spent some of my happiest times of my youth and adolescence," adding that it was there that he started reading Publishers Weekly, and that, he noted at the party, "was what first motivated me to want to be part of this strange industry of ours."

Continuing in the philanthropic spirit, Stuart told his colleagues, with whom he has over the years enjoyed an "enduring and meaningful personal professional relationship," that he wanted to begin his second half-century by "doing something special to make a difference in other people's lives." To that aim, he donated $1000 in the name of each of his guests to a charitable cause of special importance to them. The goal was 51 donations -- 50 years plus one for luck -- and that number covered his 40-plus party guests and some personal friends.