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: METHOD : Twenty - three patients suffering from severe Parkinson ' s disease ( Stages III - V on Hoehn and Yahr scale ) and , particularly bradykinesia , rigidity , and levodopa - induced dyskinesias underwent bilateral implantation of electrodes in the STN .
### Output Text:
METHOD : Twenty - three patients suffering from severe Parkinson ' s disease ( Stages III - V on Hoehn and Yahr scale ) and , particularly bradykinesia , rigidity , and <span class="chemical">levodopa</span> - induced dyskinesias underwent bilateral implantation of electrodes in the STN . 