Conservative estimates of the efficiency of detection depend on antigen abundance, precursor numbers, and LN transit time. We consider detection without blocking of egress from a dLN. When precursors are rare (A-C), slow LN transit favors the detection of rare antigen in the dLN (A lower curves, and B) but increasingly rapid transit is optimal for antigen at higher densities (A lower curves, and C). At higher precursor frequencies, when every node is likely to contain at least 1 specific cell at steady state, slower transit is optimal at all antigen densities (D-F).