Objective    To study the effect of letrozole (LE) on ovulation in patients with polycystic ovary syndrome (PCOS).     Methods    One hundred and sixtyfour patients with PCOS were divided into LE treatment group (n=68) and chloramiphene (CC) treatment group (n=96). Growth rate of follicles

serum hormone level

endometrial thickness

and cervix mucus were observed before and after treatment.     Results    The growth ra

te of follicles was 1.67 and 1.78 mm/d

respectively

in LE and CC treatment groups (P=0.14). The serum T level on the day of LH peak was 2.1±1.9 and 2.0±1.7ng/dL

respectively

in LE and CC treatment groups (P=0.93). The serum testosterone (T) level on day of LH peak and on day 3 of menses was 2.1±1.9 and 1.4±1.5 ng/d

respectively

in LE and CC treatment groups (P=0.09). The serum E

2

level on day of LH peak was 89.0±59.5 and 108.1±46.0 pg/ml

respectively

in LE and CC treatment groups (P=0.13). The endometrial thickness was 11.3±1.6 and 9.7±1.4 mm

respectively

in LE and CC treatment groups (P=0.07) .The score of cervix mucus was 11.0±1.1 and 8.3±3.1

respectively

in LE and CC treatment groups (P=0.003).     Conclusion    Letrozole can effectively induce ovulation in patients with polycystic ovary syndrome

and does not increase serum T level.