>>>Why not...
>>>
>>>

>>>use trial
>>>go top
>>>scan
>>>do case
>>>    case trial.min_sex = 'F'
>>>        replace min_f with .t.
>>>        replace min_m with .f.
>>>
>>>    case trial.min_sex = 'M'
>>>        replace min_f with .t.
>>>        replace min_m = .f.
>>>endcase
>>>endscan
>>>

>>
>>even better...
>>
>>repl all min_f with .T. for min_sex = 'F'
>>repl all min_m with .T. for min_sex = 'M'
>
>oops left out two lines
>
>repl all min_m with .f. for min_Sex = 'F'
>repl all min_f with .f. for min_sex = 'M'

Best of all:

repl min_m with .f.,min_f with .t. for min_sex = 'F'
repl min_m with .t.,min_f with .f. for min_sex = 'M'

** you don't need the scope operator ('all')
** when using the conditional ('for')