Objective: The purpose of this study was to compare the effectiveness of low-dose human chorionic gonadotropin (hCG) in the late follicular phase to induce ovulation and its endocrine response in patients who had previously failed to ovulate on clomiphene citrate (CC) alone. Design: A total of 67 patients from a private tertiary infertility clinic, who had produced a dominant follicle 12 mm or larger but 20 mm or smaller on a prior CC cycle at 100 mg but had failed to ovulate, were prospectively randomly assigned to groups. Group 1 repeated the 100 mg dose of CC but started a 200 IU hCG intramuscular injection daily when the largest follicle was 12 mm or larger mean diameter. Group 2 received a 150 mg dose of CC and both groups were monitored with transvaginal ultrasound and serum levels of E2,P4, and testosterone. Ultrasound measurements of follicle number and growth, ovulation, pregnancy rates, and serum hormonal levels were recorded and compared between the 2 groups. Analysis of variance and Student t test were used for statistical significance. Results: The low-dose hCG group had significantly higher percentage of ovulatory cycles (57% vs 7% P < .001), peak E2 levels (378 pg/mL vs125 pg/mL P < .01), and pregnancy rates (18% vs 0% P < .001). This group showed no evidence of premature leutinization from the hCG with preovulatory P4 levels less than 1.0 ng/mL and a slight increase in androgen levels. Conclusion: The use of micro-dose hCG after CC in the late follicular phase results in continued follicle growth, increased E2 levels, ovulation, and pregnancies. This treatment offers an efficient and cost-effective alternative before gonadotropin therapy for this type of patient. Objective: The purpose of this study was to compare the effectiveness of low-dose human chorionic gonadotropin (hCG) in the late follicular phase to induce ovulation and its endocrine response in patients who had previously failed to ovulate on clomiphene citrate (CC) alone. Design: A total of 67 patients from a private tertiary infertility clinic, who had produced produced dominant follicle 12 mm or larger but 20 mm or smaller on a prior CC cycle at 100 mg but had failed to ovulate, were prospectively randomly assigned to groups. Group 1 repeated the 100 mg dose of CC but started a 200 IU hCG intramuscular injection daily when the largest follicle was 12 mm or larger mean diameter. Group 2 received a 150 mg dose of CC and both groups were monitored with transvaginal ultrasound and serum levels of E2, P4, and testosterone. Ultrasound measurements of follicle number and growth, ovulation, pregnancy rates, and serum hormonal levels were recorded and compared between the 2 groups. Analysis of var Results: The low-dose hCG group had significantly higher percentage of ovulatory cycles (57% vs 7% P <.001), peak E2 levels (378 pg / mL vs 125 pg / mL P <.01), and pregnancy rates (18% vs 0% P <.001). This group showed no evidence of premature leutinization from the hCG with prevulatory P4 levels less than 1.0 ng / mL and a slight increase in androgen levels. Conclusion: The use of micro-dose hCG after CC in the follicular phase results in continued follicle growth, increased E2 levels, ovulation, and pregnancies. This treatment offers an efficient and cost-effective alternative before gonadotropin therapy for this type of patient.