Importing keys

[Andreas Hess]

Hi,

I have the following problem. I would like to import a public key by
gpg --import file.pub
and doing so, I receive the following output

gpg:  ..... no valid user IDs
gpg: this may be caused by a missing self-signature
gpg: Total number processed: 1
gpg:           w/o user IDs: 1

Must the public key be signed? Or is there another possibility to import 
public keys?
Any hint is welcome

Thanks

Andreas