In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: PURPOSE : We reviewed the results of serum testosterone and prolactin determination in 1 , 022 patients referred because of erectile dysfunction and compared the data with history , results of physical examination , other etiological investigations and effects of endocrine therapy to refine the rules of cost - effective endocrine screening and to pinpoint actual responsibility for hormonal abnormalities .
### Output Text:
PURPOSE : We reviewed the results of serum <span class="chemical">testosterone</span> and prolactin determination in 1 , 022 patients referred because of erectile dysfunction and compared the data with history , results of physical examination , other etiological investigations and effects of endocrine therapy to refine the rules of cost - effective endocrine screening and to pinpoint actual responsibility for hormonal abnormalities . 