I am strugling recoding missing values in SPSS using the graphical user interface.
I can easily recode numeric variables using the GUI and the dialogue box shown below:

But when i enter a string variable into the same dialogue box the option to define the new value as “System-missing” is not available:

Surely such a simple problem can be solved without using the syntax editor?
Im using SPSS version 19
It is because system-missing values are defined only for numeric variables. You can define user-missing values for strings. For example, recode to some unused string value, like
"99999"and set the value"99999"as user-missing afterwards.IBM SPSS Statistics 19 Command Syntax Reference, page 55: