Dear forum-driends, If someone of os could me help in this problem I wold be really grateful, I'm going crazy!! >. I was using IDL on the computer of the University, so yet installed and ready. Now I made the big step behind and now I installed IDL 8.1 on my Mac Book Pro just downloading the package "InstallIDL_Mac.pkg" , double clicking on that and following the instruction. Easy, but even if I installed a lot of library (I believe all that I need) seems that doesn't work some basic functions, for example all the STRING operations(he says: % Attempt to call undefined procedure/function: 'STRING'. % Execution halted at: $MAIN$) But I read that these functions are implemented : ---- String Operations IDL supports several basic string operations, as described below. Concatenation The Addition operator, “+”, can be used to concatenate strings together. Formatting Data The STRING function is used to format data into a string. The READS procedure can be used to read values from a string into IDL variables. Case Folding The STRLOWCASE function returns a copy of its string argument converted to lowercase. Similarly, the STRUPCASE function converts its argument to uppercase. White Space Removal The STRCOMPRESS and STRTRIM functions can be used to eliminate unwanted white space (blanks or tabs) from their string arguments. Length The STRLEN function returns the length of its string argument. --- So I suppose that these functions don't need libraries ..Have I done something wrong? I'm not able to find a solution or a clue to solve my problem and I'm literary desperate... Thank you very much to the "Saints" that will help me! :) Diego