Cynopterus brachyotis, a fruit, leaf and nectar eating bat is a common frugivorous bat in Southeast Asia. In the present study, changes in the reproductive hormones of these bats were measured. Bats were captured and blood samples were taken monthly for seven months (January to July 1997) in the surrounding areas of Universiti Kebangsaan Malaysia (UKM) campus in Bangi. The concentration of the reproductive hormones in the blood, such as testosterone (male) and progesterone (female) were measured using ELISA. The results showed that body weight and concentration of reproductive hormones was correlated with the monthly rainfall. Abundance of food during the rainy season was believed to be the important factor in influencing body weight gain and increase in reproductive hormone synthesis. Cynopterus brachyotis merupakan kelawar frugivor pemakan buah-buahan, daun dan nektar yang lazim di Asia Tenggara. Matlamat penyelidikan ini ialah untuk menentukan aras hormon yang dirembeskan oleh gonad kelawar frugivor ini, Kelawar-kelawar ini telah ditangkap dan diambil sampel darah pada setiap bulan selama tujuh bulan (Januari hingga Julai 1997) di sekitar kampus Universiti Kebangsaan Malaysia (UKM) di Bangi. Aras hormon pembiakan, iaitu testosteron pada kelawar jantan dan progesteron pada betina ditentukan dengan menggunakan kaedah ELISA. Hasil kajian menunjukkan bahawa berat badan dan aras hormon pembiakan berkait rapat dengan jumlah taburan hujan bulanan. Kelimpahan sumber makanan pada masa taburan hujan yang tinggi dipercayai merangsang pertambahan berat badan dan sintesis hormon pembiakan pada kelawar ini.