We have had experience with over 300 amniotic fluid specimens for prenatal diagnosis for the fragile X chromosome [fra(X)], and the flask method of tissue culture has been routinely utilized requiring extended tissue culture periods of 3-4 weeks. The use of the in situ clonal method of tissue culture for routine prenatal cytogenetic diagnosis of amniotic fluid cells has shortened tissue culture time and resulted in more rapid reporting; however, it has not been widely employed for fra(X) prenatal diagnosis. The simultaneous use of both methods of tissue culture has resulted in the detection of 2 cytogenetically fra(X) positive cases in amniotic fluid, with more rapid reporting and satisfactory expression of the fra(X) with the in situ clonal method. Thus, the use of the in situ clonal method of tissue culture for fra(X) prenatal diagnosis in amniotic fluid cells is feasible, faster and can serve as a more rapid cytogenetic adjunct to the newer DNA testing methods.