Thanks Safa. Although, I have one doubt. This is the code they suggest:

matrix storeMyP = J(2, 1, .)

loc n = 0

foreach variableName of varlist b c { loc n = `n' + 1 reg a `variableName' matrix storeMyP[`n', 1] = r(p) }

matrix list storeMyP

Is this code fine enough? I am running this code, but does not work:

matrix storeMyP = J(2, 1, .)

loc n = 0

foreach x in glycine alanine {

loc n = `n' + 1

regress serine `x'

matrix storeMyP[`n', 1] = r(p)

}

matrix list storeMyP

Thanks for your help