The lipid composition of three batches of single generation cysts of Globodera rostochiensis, stored dry at 4°C for 1,7 and 13 years, comprised 81%, 74% and 53% neutral lipids, 14%, 18% and 27% non-acidic phospholipids and 5%, 8% and 20% free fatty acids, respectively. Lipids in eggs from two batches of G. pallida cysts, stored for 3 and 7 years, comprised 80% and 67% neutral lipids, 15% and 23% non-acidic phospholipids and 5% and 10% free fatty acids, respectively. All batches contained the same fatty acids which were dominated by C18:l, C20:l and C20:4. The fatty acid profiles of hatched J2 of G. rostochiensis from two batches, stored for 1 and 9 years, differed only in their free fatty acid fractions. Thus, while it is not possible to determine the age of cysts by their fatty acid profile, it may be possible to use the relative amounts of the main lipid classes as an indicator of age. Four batches of hatched J2 of G. pallida were investigated, with sample A hatched during the second week in potato root diffusate, B during week 3, C during week 4 and D during weeks 5 and 6 and stored for 3.5 days (on average) after hatching. Total lipid content was 27.2%, 31.5%, 18.5% and 6.3% of the dry weight for A, B, C and D, respectively. In the neutral lipid fraction of D an increase in C18:l and to a lesser extent C18:2 was observed. In the free fatty acid fraction of sample D, the percentages of C18:l, C18:2 and C18:3 were greater but the percentages of C20:3 and C20:4 were smaller compared with sample C. Fresh early hatched J2 of G. rostochiensis were compared with later hatched and stored (for 13 days on average) individuals for their lipid content and fatty acid composition. The lipid content was 26.1% and 11.4% in fresh and stored J2, respectively. Total lipid consisted of 77% and 70% neutral lipid, 18% and 26% non-acidic phospholipid and 6% and 4% free fatty acid in fresh and stored J2, respectively. In the neutral lipid fraction of stored J2 C18:l, C16:0 and C18:0 increased, whereas C20:4, C20:l and C20:3 decreased. Therefore, both neutral lipid and free fatty acid fractions showed changes in their fatty acid profiles after long delayed hatching and/or storage in both PCN species.