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The Texas horned lizard (Phrynosoma cornutum) is protected in several states due to its apparently declining numbers; information on its physiology is therefore of interest from both comparative endocrine and applied perspectives. We collected blood samples from free-ranging P. cornutum in Oklahoma from April to September 2005, spanning their complete active period. We determined plasma concentrations of the steroids, progesterone (P), testosterone (T), and corticosterone (CORT) by radioimmunoassay following chromatographic separation and 17β-estradiol (E2) by direct radioimmunoassay. T concentrations in breeding males were significantly higher than in non-breeding males. P showed no significant seasonal variation within either sex. CORT was significantly higher during the egglaying season compared to breeding and non-breeding seasons for adult females and it was marginally higher in breeding than in non-breeding males (P=0.055). CORT concentrations also significantly increased with handling in non-breeding males and egg-laying females. Perhaps most surprisingly, there were no significant sex differences in plasma concentrations of P and E2. Furthermore, with respect to seasonal differences, plasma E2 concentrations were significantly higher in breeding females than in egg-laying or non-breeding females, and they were significantly higher in breeding than in non-breeding males. During the non-breeding season, yearling males exhibited higher E2 concentrations than adult males; no other differences between the steroid concentrations of yearlings and adults were detected. In comparison to other vertebrates, the seasonal steroid profile of P. cornutum exhibited both expected and unexpected patterns, and our results illustrate the value of collecting such baseline data as a springboard for appropriate questions for future research. We were pleased to learn that our manuscript (Ms. No.: GCE-07-52), "Effects of sex, age, and season on plasma steroids in free-ranging Texas horned lizards (Phrynosoma cornutum)" has been favorably reviewed and is still being considered for publication by General and Comparative Endocrinology. We think that GCE is an excellent venue for this work and have carefully considered the reviewers' comments in preparing our revision (for detailed responses, see 'Responses to Reviews'). OSU O K L A H O M A S T A T E U N I V E R S I T YOur revised manuscript is 30 pages long, including one table and two figures. We hope that you will find it acceptable for publication, but please do not hesitate to contact me if I can provide any additional information. Thank you for the opportunity to have our work published in GCE. What was the interval between transmitter attachment and sampling for your study?-We added the interval of transmitter attachment and added results of a correlation analysis of transmitter attachment and sampling time, see Methods LL 92-95. Lines 137-14What was the correlation between individual E2 results from the two assays?Does this give you confidence to assert that the E...

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