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: The mean plasma levels of EPO observed in AZT treated mice were appropriate for the degree of anaemia observed when compared with phenylhydrazine ( PHZ ) treated mice .
### Output Text:
The mean plasma levels of EPO observed in <span class="chemical">AZT</span> treated mice were appropriate for the degree of anaemia observed when compared with <span class="chemical">phenylhydrazine</span> ( <span class="chemical">PHZ</span> ) treated mice . 