>Sergey's answered your questions with API ways, but the volume label can also be retrieved using the ADIR() function by passing 'V' as one of the attributes.

Can you give an example using this ?
I haven't found any documentation about V attribute.

I also tried those but no volume serial was returned.

? ADIR(v,'c:','DV')
DISPLAY MEMORY LIKE v
? ADIR(v,'c:\','DV')
DISPLAY MEMORY LIKE v
? ADIR(v,'c:\*.*','DV')
DISPLAY MEMORY LIKE v
? ADIR(v,'c:\*.*','V')
DISPLAY MEMORY LIKE v