Random amplified polymorphic DAN markers were characterized for three taxonomically problematic Penicillium species : P. aurantiogriseum var. Aurantiogriseum, P. verrucosum and P. puberulum, as well as for 25 species of mono, bi-, and terverticillate Penicillia. The relationships among mono, bi-, and terverticillate Penicillium species were determined from these RAPD markers. Eight species from mono-, eight from bi-, and nine from terverticilate Penicillia were examined. With 14 randomly chosen 10-mer primes, a 310 character by 25 species matrix was generated. Phenetic analysis separated the 25 species into three genetically distinct groups that correspond to the different arrangements of penicilli (mono-, bi-, and terverticillate). The results of this study suggest that P. aurantiogriseum var. aurantiogriseum, P. VERRUCOSUM, AND P. puberulum represent genetically distinct species, and that P. vulpinum should be included in terverticilate Penicillia. Phenogram branching patterns indicated that biverticillate species are genetically more similar to monoverticilate species than they are to terverticillate species.