Basement Toilet Gurgle Shower Geiser!

I've done a little reading of some of the other posts and think that I either have a clog or venting issue, but I need to ask the pros because this one has me stumped!

I live in a 1956 SFH with 2 upstairs toilets and a full bath in the basement. I came home the other day to a soaking wet basement floor. The facts:

-The majority of the water in the toilet was no longer in the toilet
-There is a "splatter pattern" of a dark brown substance in the shower that looks like a lot of water came up through the shower drain (gross!)
-There is a gurgle now in the downstairs toilet when I flush the upstairs toilet.

Any ideas? If it is venting, is that something that I can fix myself (I get the concept of venting but I'm not sure how to fix it).

Thanks!

The nature of your question indicates to me that you should call a plumber. In the mean time, do not dump chemicals in the drain. If you already have, tell the plumber what, when, and how much you put in. Chemicals will not fix many drain problems, certainly not the large ones, and besides damage to the drain lines, create a dangerous condition for plumbers to work in. You don't have the knowledge, experience, or equipment to deal with this yourself.

Calling a pro?

Thanks, but is there anything that I could try on my own?

JoeFrankBillyBob Where are you located?

Is it in a frozen wasteland or, the sunny south? You just might have a frost closure on a vent.

Washington DC

I'm in Washington DC - it's been quasi cold here as of late!

Where would my vent be located? (near the toilet, corner of house) - obviously outside, right?

It would be through the roof. In D.C. I would doubt you have frost closure... This problem usually requires single digit, or, worse temps to occurr. You probably have a drain line problem.

Drain Line problem

Okay I'll byte...

How do I fix a drain line problem? Take a huge snake in through the toilet?

Could it be that my neighbors are also experience this, or is it more than likely just me? Neighbors are about 50 feet away in another SFH.

You call a professional plumber who can auger the drain with professional equipment. You should not even consider attempting this yourself. The size and power of the auger required to do a complete job is not for a novice. Even pros sometime break the auger or hurt themselves. There are times, and this is one of them, you bite the bullet and pay the man. It will probably save you money in the long run. "A man's got to know his limitations." Dirty Harry