specifically this solution must foster strong pplx accumulation over a minimum time period and very thorough pplx distribution throughout the treated tissue this goal is achieved using a 5 aminolevulinic acid ester e ala such as that defined in the preamble characterized in that the concentration c of e ala in the solution is less than 1 and ranges from 0 01 to 0 5 0 01 u2266 c u2266 0 5 it has been shown in practice that use of a very low concentration of e ala in the solution increases pplx synthesis and homogenizes distribution throughout the cellular layers while at the same time greatly reducing secondary toxicity of the solution to the treated cells this becomes even more important because when treating a tumor with dynamic phototherapy the rapid photobleaching reduces pplx concentration complete destruction of the tumor implies an elevated initial accumulation of intracellular pplx and thorough distribution throughout the layers of the tumor advantageously the ala e ala ester producing the best results is hexylester hydrochloride ala h ala the solution is preferably produced by dissolving the ala e ala ester in a solvent compatible with human or animal organisms said solvent is advantageously selected from the following substances sterilized filtered water physiological nacl solution phosphate buffer solutions with phosphate or alcohol in its preferred form the solution comprises a component for adjusting the ph to a physiological value ranging from 4 8 to 8 1 in an advantageous form the solution may comprise a complementary substance to prevent the transformation of the pplx into a heme by iron complexing in the living cells said complementary substance may be an edta ethylene.