The binding of serum albumin and lipoprotein with chlorin p(6) and purpurin 18, two structurally related chlorins, has been studied to understand the role for these proteins as endogenous carriers for these drugs. As a drug carrier a protein may aid in selective delivery of a drug to a tumor region. Binding with serum albumin may result in accumulation of the drug in the stroma of the tumor cell and lead to a reduction of cellular uptake of photosensitizers. However, it is possible that this factor may not be a problem for cellular uptake of chlorin p6 and purpurin 18 by the tumor tissues, since it binds more efficiently with low-density lipoprotein when it become more lipophilic, indicating that the principal carriers for these molecules are lipoproteins. Since the tumor tissues contain numerous lipoprotein receptors, chlorin p6 and purpurin 18 could be internalized more efficiently in tumor cells.