Gonadal progestins from fetal, juvenile, pregnant and non-pregnant Masai giraffe (Giraffa camelopardalis) were extracted, purified by TLC and measured by GLC or by competitive protein-binding assay. Progesterone was found in fetal ovaries and in a fibrotic CL from a nearterm fetus as well as in CL from juvenile animals. In pregnant animals, luteal progesterone probably increased with the duration of gestation. The values of 20β-hydroxyprogesterone were higher in juvenile giraffes than in the fetus or during early pregnancy. No 20β-hydroxyprogesterone was detectable in a CL from late pregnancy or a CL from a non-pregnant giraffe. The values tended to be inversely related to the progesterone levels. Detectable levels of 17α-hydroxyprogesterone were present in the fetal ovary, juvenile CL and in one pregnant animal with an early preimplantation blastocyst. In the later stages of gestation, the hormone levels were too low to be detected by TLC. Thus, it seems that the CL present in the ovaries of fetal and juvenile giraffes are endocrinologically active and similar in function to the CL of adult female giraffes.