There is limited published literature on the potential impact of diluent and drug concentration on the pH and osmolality of IT chemotherapy preparation. Most cancer centers conventionally prepare IT chemotherapy with 5 mL of preservative diluent normal saline, irrespective of the specific drug or dose used. The conventional practice means that most methotrexate preparations are likely to have comparable pH and osmolality to CSF. In contrast, cytarabine preparations may show significantly higher pH than the CSF, while thiotepa preparations generally have lower osmolality than the CSF.