Pee!!

[GrifTheGreat]

Its normal behavior. Don't handle your frog too much. It can make them sick. The oils and salts on your skin can damage their skin. They can even be poisoned by the oils. Always wash your hands thoroughly with a very mild cleanser and rince well. Then dry your hands completely and wet them with de-chlorinated water or spring water whichever you use for your frog. This reduces the risk greatly of them being harmed due to you removing the oils. Always handle them with wet hands.

That being said you should also know that handling your frog frequently causes stress. Stress needs to be kept at as low a level as possible. Stress is one of the main reason captive frogs die if not the number one reason. Be careful

[NetworkLabs]

Now you have to handle with dechlorinated wet hands?!? Never knew that...

[wesleybrouwer]

What would be the reason handling a frog?
Best thing for them is to be left inside their viv.
If you like a pet that can be handled, maybe a frog won't be the right choice.
Like already said, it puts the frogs health in risk while it isn't necessary at all.
Besides cathing out juveniles or for treatment i never get my frogs out.

The peeing actually is mostly water, just a very small percentage is urine.
It's part of the defence mechanism indeed.
By squeezing out the water they hold, they make theirselfs lighter and therefore they will be able to move faster and jump further.
The weight reduction can be as much as 50% of the total body weight.
In my point of view, a frog never gets used to handling, it's not like you can tame a frog.
Maybe the great amount of topics on sick, deseased, stressed or even death frogs could be because of the handling by most people,
reading the frogs are often taken out at least once a week for cleaning a cage, i guess it's not the most suitable way to keep them.
Stress is probably cause of death number 1, so you might like to avoid causing stress as much as possible.

[BeckyM]

You can also hold them with rubber/nitrile gloves on.

I used to hold my frog all the time. Then I read something about it potentially hurting him and I stopped. five years later, he's still here. Must not have stressed him out too terribly. :P (He always got revenge on me by crapping on my hands. >_>)