Provided herein are improved methods of photodynamic treatment and diagnosis of cancer and non-cancerous conditions in the gastrointestinal tract, e.g. in the colon, and in particular hyperosmotic enema preparations for use in such methods. The enema preparations comprise a photosensitizer which is 5-aminolevulinic acid (5-ALA) or a precursor or derivative thereof, e.g. a 5-ALA ester, in combination with at least one hyperosmotic agent. The methods and preparations herein described are particularly suitable for use in photodynamic methods of treating and/or diagnosing colorectal cancer.
