A case of plaque stage mycosis fungoides and one of parapsoriasis en plaque were treated with topical PUVA therapy using a monofunctional furocoumarin derivative, 4,6,4'-trimethylangelicin (TMA). Both patients showed complete clearance of eruptions within 16 treatments. The therapeutic effectiveness of TMA was confirmed by the fact that those eruptions exposed to UVA alone, without TMA application, showed slower and less significant improvement. Histologically, dermal infiltrates of mycosis cells and associated epidermotrophism disappeared almost completely in response to TMA PUVA. No side effects or changes in values in laboratory examinations were observed during treatment.