The presence of vertebrate-like sex steroid hormones (VLSHs), such as progesterone, testosterone and estradiol, has been reported in many invertebrate phyla, but especially so in molluscs and echinoderms. While the synthesis and physiological function of sex steroid hormones in vertebrates are well-known, much less is known in invertebrates. In echinoderms, the sister taxon to the chordates, the levels of many VLSHs appear to change in relation to the reproductive cycle in the ovary and the pyloric caeca which suggests that VLSHs are involved in reproduction. However, the specific role of steroid hormones in reproduction and the regulation of their synthesis in echinoderms is not yet clear and still debated. Therefore, this study aimed i) to investigate the steroidogenic activity in the New Zealand sea star Patiriella regularis ovary and pyloric caeca in vitro during the reproductive cycle, and ii) to identify steroidogenic enzyme transcripts by transcriptome analysis of the sea star ovary. Target tissues were incubated with or without pregnenolone or androstenedione during each stage of the reproductive cycle and vertebrate-like sex steroid hormones (progesterone, androstenedione, testosterone and estradiol) were identified in the incubation media after incubation using liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry. The ability of both ovary and pyloric caeca to convert pregnenolone to progesterone and androstenedione to testosterone was demonstrated, indicative of hydroxysteroid dehydrogenase activity in sea star. The concentration of testosterone in androstenedione-supported incubations appeared to be higher in ovary than in pyloric caeca, whereas stage of the reproductive cycle seemed to not have an effect. However, it remains unclear whether or not these conversions resulted from steroidogenic enzymes similar to those found in vertebrate steroidogenic tissues. Work is currently in progress to identify steroidogenic enzyme transcripts by analysis of transcriptome sequencing data from the sea star ovary.