kako si

1. how are you?
   Zdravo, Marko, kako si? – Dobro, a ti? — Hi, Marko, how are you? – Fine, and you?
   Dugo se nismo čuli, kako si? — We haven't talked in ages, how are you?

Informal, addressed to one person you call "ti"; the usual answer is "Dobro, a ti?".