Abstract: For monitoring an environmental parameter such as the level of nuclear radiation, at distributed sites, bar coded sample collectors are deployed and their codes are read using a portable data entry unit that also records the time of deployment. The time and collector identity are cross referenced in memory in the portable unit. Similarly, when later recovering the collector for testing, the code is again read and the time of collection is stored as indexed to the sample collector, or to a further bar code, for example as provided on a container for the sample. The identity of the operator can also be encoded and stored. After deploying and/or recovering the sample collectors, the data is transmitted to a base processor. The samples are tested, preferably using a test unit coupled to the base processor, and again the time is recorded.