Metabolism of PGE-2 and PGF-2 alpha by cytosolic fractions (100 000 g supernatant) of rabbit uterus, oviduct and lung was measured in vitro. Metabolism of PGE-2 was greater than that of PGF-2 alpha for oviduct and uterus. After an ovulating injection of hCG metabolism of both PGE-2 and PGF-2 alpha by lung and uterus declined linearly up to 72 h (during the time of ovum transport). The amount of PG metabolism by the oviduct did not change significantly during this period, but the percentage changes of PGE-2 and PGF-2 alpha metabolism from oestrous values did differ, and perhaps indicated a change in the ratio of intracellular PGs. No change of metabolism of either PG by lung, uterus or oviduct occurred at 24 or 72 h after an injection of 250 micrograms oestradiol cyclopentylpropionate given concomitantly with the hCG (a treatment regimen which causes 'tube-locking' of ova). However, progesterone treatment, in a regimen known to cause accelerated transport of ova through the oviduct, caused significantly enhanced metabolism of both PGE-2 and PGF-2 alpha by uterus and oviduct, but not lung, 30 and 48 h later except for PGE-2 by uterus at 30 h. These results suggest that changes in metabolism of PGE-2 and PGF-2 alpha by the oviduct may be involved in the mechanisms controlling ovum transport.