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: Hepatitis B immune globulin ( HBIG ) and immune serum globulin ( ISG ) were examined in a randomized , double - blind trial to assess their relative efficacies in preventing type B hepatitis after needle - stick exposure to hepatitis B surface antigen ( HBsAG ) - positive donors .
### Output Text:
Hepatitis B immune globulin ( HBIG ) and immune serum globulin ( ISG ) were examined in a randomized , double - blind trial to assess their relative efficacies in preventing type B hepatitis after needle - stick exposure to <span class="chemical">hepatitis B surface antigen</span> ( <span class="chemical">HBsAG</span> ) - positive donors . 