$Error log transformed

Dear All, I would like to model my data log transformed. So far, I already found some suggestions for this problem here but none of them worked in my case - probably I did sth. wrong. I would be very happy if someone could help me with changing my error model, which I assume has to be changed. (I also assume that the dataset has to be changed from DV to LOG(DV)?) So, here is the code I used so far (not log transformed): $ERROR IPRED = F ;IPRED drug in the central compartment IF (CMT.EQ.5) IPRED = A(5) ;IPRED second drug in 5th compartment DEL=0 IF (IPRED.EQ.0) DEL=0.0001 W = F IRES = DV - IPRED IWRES = IRES /(W + DEL) Y = IPRED + IPRED * EPS(1) ; error drug in the central compartment IF (CMT.EQ.5) Y = IPRED + IPRED * EPS(2) ; error second drug in 5th compartment It would be great to get some help. Thanks! Katrin