Thermal ink jets (TIJ) have been used as a micro-delivery system for the deposition of cDNAs onto modified glass supports. We have modified TIJ heads and firing electronics, designed for the printing of ink, to form the core of a micro deposition system that efficiently, reliably and accurately deposits large numbers of cDNAs into tightly packed arrays. Data will be presented demonstrating that these arrays, generated by the TIJ process, generally perform similarly to arrays generated using conventional pen technology but offer advantages in feature quality, control of spot size and large-scale manufacturing. Quality assurance data from the drop detect and inspection systems used to qualify production runs will be presented as well as results from experiments using multiple TIJ fires to produce variable feature sizes. Lower limit of detection and two-colour competitive hybridization data collected from a new high-speed, high depth of field, autofocus scanner (under development) will also be presented.