The Bottom Line : Many men still cotton to PJs, but sans the tops. (These are not their fathers’ pajamas.)

Ricky Ricardo and Rob Petrie never went topless. And Frasier Crane always keeps his shirt on, too.

But real men don’t always do jammies.

Some sleep in the buff--or in briefs, boxer shorts, sweats, even nightshirts. Of those who do wear PJs, many either sub out the matching top for a T-shirt or go bare. But whatever their bedtime get-ups, men--and the women who shop for them--have been snapping up pajamas lately, particularly the bottoms.

“There are still some traditional men who wear the whole pajama set, but the biggest growth is in separates,” says Sally Koellner, a Dallas-based buyer of men’s sleepwear for JC Penney. While sales of sets are up 25% over the last year, she says, sales of separates have jumped 35%--even though they’re more costly.

Tops sell for $20 to $25, pants for about $20 and pajama shorts--a plush take on boxers--for about $15. Comparable PJs sold in sets go for about $30.

The separates are appealing because they look nothing like the piping-trimmed tops and flimsy bottoms often associated with traditional pajamas. They lean more toward casual wear, with baggy cuts, sturdy fabrics and drawstring waistbands.

Koellner says her husband isn’t shy about leaving the house to do an errand in his bottoms and a T-shirt. “When he comes home from work, he puts them on and doesn’t take them off until he goes to work the next day. He can even go into 7-Eleven to pick something up if he wants.”

“Men really do tend more toward just wearing the bottoms,” says David Laliberte, public-relations associate for the Fashion Assn., a New York City-based apparel-industry organization.

J. Crew, with a mail-order business and 28 stores nationwide, is another of the growing number of retailers that sell pajamas as separates. The company offers PJ pants in bold plaid flannel for about $25, among other styles.

Whittier resident Mark Haner prefers similar flannel styles from L.L. Bean. For a new father, he says, they’re a necessity for midnight runs to the crib. “It’s not like you can ask him to wait a minute while you get dressed,” Haner says.

But some men can’t bear to wear anything but traditional PJs. Will Utay of West Hollywood has been known to pack his for a camping trip.

“When I came out of my tent in my maroon Jacquard stripe pajamas, people were in hysterics,” recalls the actor, who plans to take a more outdoorsy-looking flannel pair on his next outing.

“Growing up wearing pajamas, I remember a sense of comfort and security. It’s difficult for me to sleep if I am not wearing them,” he says.