The investigation of choice to differentiate Mullerian agenesis from testicular feminization syndrome in a case of primary amenorrhea is:

Turner syndrome (gonadal dygenesis) is the most common cause of primary amenorrhea. In patients of Mullerian agenesis the karyotype is 46 XX. Whereas in testicular feminization syndrome (androgen insensitivity syndrome) it is 46 XY. Laparoscopy will reveal absent uterus in both the cases but in Mullerian agenesis there is presence of ovary and in testicular feminization syndrome there will be testes (in inguinal region). But just for a diagnosis, laparoscopy is not required. USG would reveal the same finding and help in diagnosis but the investigation of choice is karyotyping .