All seed coming into CIMMYT either through regular shipments or hand-carried must go through the SHU. If seed is delivered directly to a program, packages must NOT be opened but taken to the SHU laboratory. SHU staff will record the seed's arrival and notify via email the person to whom it was sent. The seed is then sampled and tested. H the material arrives during the planting cycle, it is kept under observation for 48 h and released if no pathogens are detected. At other times, the seed is kept for three weeks for testing purposes. There are three possibilities with respect to test results: a) The seed has been properly disinfected and is pathogen-free. b) The seed has not been properly disinfected but is free of pathogens of quarantine concern in Mexico. In this case, SHU will recommend the appropriate treatment. c) The seed is carrying a pathogen(s) quarantined by Mexico's plant protection authorities. H the material is very valuable and the pathogen can be destroyed without risk of dispersal, the seed remains under strict SHU control and is planted under specific conditions until it is determined that the risk no longer exists. However, if the risk canriot be eliminated, the seed is incinerated or returned to the sender. Seed meeting the requirements described in points a) and b) may be taken away by a program-designated assistant only and planted exclusively in the introduction blocks, without exception. The purpose of this procedure is to detect and destroy any pathogen that may have not been detected in laboratory tests. When the seed is taken out of the lab and the head of the program decides the specific quarantine plot where it will be planted, he/ she should send this information to the lab.