The speed and accuracy with which Fused Deposition (FD) ABS plastic components can be made gives this rapid-prototyping technology unique potential as a new method for manufacturing complex structural components. Quantitative relationships between the FD process variables and the resulting mechanical properties are needed for intelligent manufacture of polymer components with tailored strength properties. This work examined the influence of the process variables on the resulting microstructure (void and interface bond length densities) of two configurations with uniaxial fiber orientation. The results showed the void and interface densities to be strongly dependent on the fiber-to-fiber gap and extrusion flow rate settings; the influence of extrusion and envelope temperatures is much smaller. The skewed fiber configuration exhibited the lowest void density but also the lowest interface density values. However, the difference observed in the values for the interface density were not as big as for the case of the void density. An investigation of the influence of the process variables on the interface bond strengths and the tensile behavior of pre- and post-extruded fibers as a function of loading rate and test temperature is in progress.