How long should I wait for the response of the referee? i wrote a message to the Editor to inquire about my
revision sent about 4 months ago.  He informed me yesterday(March 20th, 2014)
that my manuscript has already completed 1 review.
However, we are still awaiting the last report.
from the remaining referee. My question is How long
should I wait for the response of the referee? and what do you advise me to do?
n.b. the journal belongs to Springer
Best regards
i wrote a message to the Editor to inquire about my revision sent about 4 months ago. He informed me yesterday(March 20th, 2014) that my manuscript has already completed 1 review. 


Since you have contacted the editor and they looked into it (and perhaps pinged the reviewer with a reminder), I don't see that there is much else you could do at this point (other than something drastic like withdraw, which would be entirely unjustified after four months).


  However, we are still awaiting the last report. from the remaining referee. My question is How long should I wait for the response of the referee? 


As long as it takes.


  and what do you advise me to do?


You've just contacted the editor and gotten a response. My advice now would simply be to be patient. Try to put it at the back of your mind and focus on other work. (And don't message the editor again for another few months; have faith in them to do their job.)


  4 months for secondary revision is too long no?? 


In many fields, unfortunately, no.