Bleach solution of some kind. I don't know what it'll do to the wood in terms of looks, but who cares, it's plywood. Also, you can buy cleaners called Nature's Miracle, with enzymes, that do a great job.

Oil based Kilz will seal the wood. It must be the oil based. You may have issues with woodwork and walls also. Dogs and cats both tend to mark vertically. It wouldn't hurt to prime the walls in the whole house with Kilz prior to painting. Even a hint of odor can kill a sale.

excuse me...previous TENANT. Not owner.

Thanks for the replies thus far. What is everybody's thoughts on white vinegar?

I don't know what area you are in but if you can open all the windows to air it out well, the smell may be gone. I think the enzyme products made for dog/cat pee are really good. You mix some in a bucket of water and mop the plywood and let it air-dry. Leave the windows open, if possible, the odor should be gone.

I don't think the vinegar will do it alone. If the plywood isn't stained, the odor is probably in the air. Spray with Febreeze. Nothing takes care of odors better than fresh air. Open the windows.

Good luck,
Jane

Go to a pet store and buy a small black light. Use it at night and you will be able to find the pet stains.

Vinegar won't help. Bleach won't help. Febreeze is a temporary at best solution. The enzyme solutions might work, but you have to saturate the area with the enzyme product, and even then, I wouldn't trust it enough to lay carpet over it.

For a permanent solution, you have to seal the drywall and the wood. Postpone the carpet installation and fix the problem first (is my advice).

An acquaintance who once managed an apartment complex said that she used a regular sealant & then a heavy coating of paste-type floor wax before she re-carpeted any of the units;
sort of belt & suspenders strategy.

We too had a problem and used Kliz product on the floors and walls. Talk to your paint dept. Other products just don't seem to take care of the problems. I agree, postpone the installations, and paint first. Will take awhile to dry, and may take more than one coat. It took us a month to do the room and when we told the person who bought the property, she checked it out and was very happy.

I'd go ahead Kilz it first like everyone else says. Smells always seem to show up during wet and warmer weather. I wouldn't chance the expense of installing carpet and the smell coming back in a few months.

I have to tell you - when we bought our house the previous owner must have locked her cat up in one of the bedrooms and that cat used the carpet as part litter box (if you know what I mean). It was horrendous - you literally couldn't breathe in that room and we needed it for my son's room. We couldn't afford new carpet, but having had dogs for years and have used it in their kennels we sprayed/saturated the carpet with Odo-ban (Sam's Club & you can now buy it at Home Depot) and opened the windows.
Believe it or not - it worked. No lie. The smell we gone. I was surprised it worked as well as it did. Friends have also used it with their cats/dogs in their houses as well - so I highly recommend it. (And this carpet was overtop of hardwood floors - which 5 years later I refinished).