Trisomic rice (Oryza sativa L.) lines are plants that have an additional chromosome [2n=2x=25 vs. 2n=2x=24 (normal)].  Presence of a third chromosome alters segregation ratios which makes trisomic lines helpful for a) locating a gene on a particular chromosome, b) verifying the independence of linkage groups, c) associating the genetic linkage groups with individual chromosomes or d) incorporating alien variation.  In addition to primary trisomic lines with an additional complete chromosome, there are secondary trisomic (double chromosome arm) lines and telotrisomic (single chromosome arm) lines.  In an effort to incorporate the IR36 trisomic series into the US germplasm collection, all twelve IR36 primary trisomic lines, secondary trisomic (1S.1S, 2S.2S, 5S.5S, 6S.6S, 6L.6L, 7S.7S, 8S.8S, 8L.8L, 11S.11S, 11L.11L, 12S.12S) and telotrisomic (2L, 3L, 5L, 7S, 9S, 12S) lines were obtained from the International Rice Research Institute, Philippines.  These lines were grown in the rice quarantine greenhouse at Fayetteville, Arkansas and the supposed trisomic plants were identified based on morphology and heading date.  As part of the subsequent field grow-out in Stuttgart, AR, panicles were collected for cytogenetic analysis from putative trisomic plants.  To date, the nine primary, four secondary, three telo- trisomic lines have been confirmed by cytological observation.  Questionable trisomic plants are being verified with chromosome arm specific BAC clones using in situ hybridization procedures.  When this project is complete, all twelve primary trisomic lines, and a secondary trisomic and/or telosomic line for at least one chromosome arm representing each of the twelve rice chromosomes should be available for distribution through the USDA-ARS Genetic Stocks-Oryza collection.