The gut protozoan parasite, Giardia lamblia (Assemblage A), has 5 major chromosomes, 1 of which is 2 Mb, as determined from gel separations of whole chromosomes. We originally published a physical map of this chromosome and, now, using the sequence data from 46 chromosome-specific probes, have produced a sequence map of the 2 Mb chromosome. Comparison of the probe sequences with the Giardia genome database ( http://GiardiaDB.org) has identified 4 scaffolds (CH991771, CH991780, CH991782, and CH991767) belonging to the 2 Mb, Assemblage A, chromosome. Because of the density of probe sequences, we have been able to predict the orientation of the scaffolds and have identified erroneous inclusions in scaffold CH991767. Exclusion of erroneously included sequences resulted in a 1.96 Mb chromosome sequence. This study brings together experimental data and the GiardiaDB data to compile the sequence of a whole chromosome.