FLASH (Flow-Log Analysis of Single Holes) is a computer program for the analysis of borehole vertical flow logs. The code is based on an analytical solution for steady-state multi-layer radial flow to a borehole. The code includes options for (1) discrete fractures and (2) multi-layer aquifers. Given vertical flow profiles collected under both ambient and stressed (pumping or injection) conditions, the user can estimate fracture (or layer) transmissivities and far-field hydraulic heads. FLASH is coded in Microsoft Excel with Visual Basic for Applications routines. The code supports manual and automated model calibration.