Thanks to those who replied. Someone suggested I use Jas to do my analysis, which is fine by me. However, in trying to keep things as current as possible I am simulating my events with geant4 using a stripped down version of lcdroot named lcdg4 ( from Robert McIntosh at NIU ). When I try to analyze the resulting sio file I get an error message along the lines of: hep.lcd.util.event.EventException: Key TrackerHits not found in EventHeader at hep.lcd.io.jas.sio.LCDGismoEvent.get(LCDGismoEvent.java:27) at hep.lcd.util.event.AbstractLCDEvent.getTrackerHits(AbstractLCDEvent.java:17) I was assumming there was an inconsistency between the output from gismo vs. that of geant4, but perhaps it is something else? -Brandon -- Brandon Drummond <[log in to unmask]> UTD-High Energy Physics