Because of the way things are, #MACRO and #IFDEF do not play well together in PICAXE basic. To create a macro which does one thing or another depending on a #DEFINE definition can seem impossible. For example, neither of the following two will pass syntax check -

Code:
#Macro PrintLetter
  #IfDef PRINT_A
    SerTxd( "A" )
  #Else
    SerTxd( "X" )
  #EndIf
#EndMacro
Code:
#IfDef PRINT_A
  #Macro PrintLetter
    SerTxd( "A" )
  #EndMacro
#Else
  #Macro PrintLetter
    SerTxd( "X" )
  #EndMacro
#EndIf
The solution is to code things slightly differently.

Here we specify two separate #MACRO's, 'PrintLetterA' and 'PrinteLetterX', to do the two different things we require. And then we use #IFDEF to selectively #DEFINE what 'PrintLetter' actually is -

Code:
#Define PRINT_A

#IfDef PRINT_A
  #Define PrintLetter PrintLetterA
#Else
  #Define PrintLetter PrintLetterX
#EndIf

#Macro PrintLetterA
  SerTxd( "A" )
#EndMacro

#Macro PrintLetterX
  SerTxd( "X" )
#EndMacro

Do
  PrintLetter
Loop
That code can be simulated in PE6 and will show the affect of including or removing the '#Define PRINT_A'.

Because #MACRO commands only generate code when invoked, no matter how much code is in each of the two #MACRO's, only the code in the one used will be included in the compiled program.

If there is a lot of common code required within each #MACRO; it may be possible that the common code can be moved out into its own #MACRO and then a macro expansion used in each #MACRO -

Code:
#Macro Prefix
  SerTxd( "Prefix" )
#EndMacro

#Macro PrintLetterA
  Prefix
  SerTxd( "A" )
#EndMacro

#Macro PrintLetterX
  Prefix
  SerTxd( "X" )
#EndMacro
One thing to note: If the macros have parameters, then those parameters must also be included in the #DEFINE statements as well.

If that is not done there will be "( expected" errors generated.

Code:
#Define PRINT_A

#IfDef PRINT_A
  #Define PrintLetter(n) PrintLetterA(n)
#Else
  #Define PrintLetter(n) PrintLetterX(n)
#EndIf

#Macro PrintLetterA(n)
  SerTxd( "A", #n )
#EndMacro

#Macro PrintLetterX(n)
  SerTxd( "X", #n )
#EndMacro

Do
  For b0 = 1 To 10
    PrintLetter(b0)
  Next
Loop
Again, the effect of including and removing '#Define PRINT_A' can be tested using simulation under PE6.