My ILs visited this past week and about 3 days into the visit, one of my cats started peeing on anything of my MILs that he could. A canvas bag, a fleece, her rain coat, etc. I think there were 5 things in all that I had to try to save.
He's had pee'ing issues before when we got him from the shelter, but hasn't had any problems in almost a year.
We're going to the vets tomorrow, but I know you ladies are experts--this is more likely behavioral than medical, right? If he had an infection of some kind, he wouldn't be likely to be targeting particular things? He's never peed on her stuff before though. She doesn't have any pets or anything like that.
Re: Cat pee'd on only MIL's stuff...
I'd get him into the vet ASAP to rule out anything medical and then go from there.
The FAQ has some good info.
Ditto these thoughts. My big gray kitty has issues with stress (although you'd never think it since he's such a social cat). Feliway plugins help a lot. And when we're going into something that I know will be stressful for him (like houseguests) he gets a comfort collar (read reviews about these on amazon first though since lots of people seem to have issues with them).