The invention provides anionic water-soluble tetracyclic and pentacyclic bacteriochlorophyll derivatives (Bchls) containing at least one, preferably two or three, negatively charged groups and/or acidic groups that are converted to negatively charged groups at the physiological pH, preferably Bchls having a group COO , COS , SO3 , PO3 , COOH, COSH, SO3H, and/or PO3H2 bound through an ester or amide bond to one or more of the positions 17 , 13 , and 3 of the tetracyclic or pentacyclic Bchl molecule, for photodynamic therapy and diagnosis.