Multiple postgresql functions in a single transaction

Hi,

I have two postgresql functions. One function is calling another function
for certain value. I want that these two functions work under single
transaction so that even if the value gets generated in the second function
and the first function that calls the second function fails. Then the value
generated in the second function should also roll back.

Please let me know if we can execute two functions of postgresql in a single
transaction.

Thanks,
Jyoti Seth