Thirteen resistant selections of S. tuberosum hybrids bred in the U.S.A. and Europe and 44 diploid clones derived from S. vernei, S. spegazzinii, S. neohawkesii, and S. sanctaerosae each with resistance to one or more pathotypes of H. rostochiensis were tested for their resistance to three Peruvian populations of this nematode. Only one diploid clone of S. sanctatrosae was found to be resistant to the three populations of nematodes, but several clones were resistant to one or another of the nematode populations. More clones were found to resist the nematode population collected near Cuzco than those populations collected near Huancayo or Otuzco. Morphometric measurements of body length, stylet length, and distance of median valve to excretory pore, of second stage larvae showed great variation and no clear difference among the three populations. The measurements obtained were closer to pathotype E from England than to any other recognized pathotypes. © 1973 Springer.