Bi-directional liquid sample handling system

An automatic liquid transfer system includes a horizontally translatable table and a pipette that is translatable both vertically and horizontally in a direction transverse to the axis of translation of the table. The table accommodates one or more titer trays having a multiplicity of receptacles to be filled, or holding liquid samples to be diluted, transferred, or aspirated, and a rack housing plural rows of disposable tips. Between each cycle in a liquid transfer process, a fresh tip is picked up by the pipette and used to transfer liquid in a sterile manner from a sample or diluent source to a well in the titer tray, or from one well to a different well anywhere on the one tray or to a receptacle in a different tray, where it is mixed with diluent. Thereafter, the tip is discharged back into the rack to maintain sterile conditions during the process and a new tip is installed.