The present invention provides manipulation of spacing between microdroplets flowing in a microfluidic system. The manipulation includes increasing and/or decreasing spacing between a pair of adjacent droplets of a sample fluid flowing in an immiscible carrier fluid within a main microfluidic channel. The main microfluidic channel includes a region having one or more side branch channels. The spacing between the pair of droplets flowing through the region can be increased or reduced with either the addition of or removal of immiscible carrier fluid between the adjacent droplets via at least one of the side branch channels, wherein the pair of droplets remain intact while flowing through the region and continue to flow within the main microfluidic channel downstream of the region.