Methods of increasing the amount of polyunsaturated fatty acids (PUFAs) in the total lipid fraction and in the oil fraction of PUFA-producing, oleaginous eukaryotes, accomplished by modifying the activity of peroxisome biogenesis factor (Pex) proteins. Disruptions of a chromosomal Pex3 gene, Pex10p gene or Pex16p gene in a PUFA-producing, oleaginous eukaryotic strain resulted in an increased amount of PUFAs, as a percent of total fatty acids and as a percent of dry cell weight, in the total lipid fraction and in the oil fraction of the strain, as compared to the parental strain whose native Pex protein was not disrupted.