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 numbers of BFU - e and the percentage of bone marrow erythroblasts observed were comparable in AZT and PHZ treated mice with similar degrees of anaemia .
### Output Text:
The numbers of BFU - e and the percentage of bone marrow erythroblasts observed were comparable in <span class="chemical">AZT</span> and <span class="chemical">PHZ</span> treated mice with similar degrees of anaemia . 