In vitro studies on monkey luteal cell function were further extended. Dissociated luteal cells from monkey corpus luteum were studied utilizing either short-term (3h) or long term (10d) cell culture systems. Short term studies have shown that the integrity of LH/hCG receptors is maintained after 10 min exposure to trypsin. Long-term studies have indicated that steady high levels of progresterone synthesis can not be maintained by luteal cells even when the culture medium is augmented with steroid precursor or other nongonadotropic hormones. Although under experimental conditions the endogenous estrogen levels can be suppressed, it has no effects on the declining patterns of progesterone synthesis.