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 effects of a 6 - hour infusion with haloperidol on serum prolactin and luteinizing hormone ( LH ) levels was studied in a group of male subjects .
### Output Text:
The effects of a 6 - hour infusion with <span class="chemical">haloperidol</span> on serum prolactin and luteinizing hormone ( LH ) levels was studied in a group of male subjects . 