Some experts have argued that the arrival of crack stimulated an increased availability of guns among juveniles and, further, that this greater availability of guns was responsible for the sharp upswing in juvenile homicide experienced in the United States in the mid-1980's. This study used city-level data on crack arrests and gun-related juvenile homicide to fit a change-point version of one model of innovation diffusion. In most large American cities, the diffusion process for crack cocaine experienced an onset of dramatic growth that was followed by a similar, slightly slower growth in gun homicides committed by juveniles. The study used cluster analysis to find that the spatial patterning of the two processes was similar, starting on the east and west coasts and working its way toward other regions of the Nation. Gun use in homicide among slightly older offenders (ages 18-24) also experienced a change at roughly the same time as the juveniles, but the rate of diffusion was considerably milder than for the younger group; offenders ages 25 or older generally showed no growth in gun-related homicide whatsoever. In addition, there was no detectable surge in juvenile non-gun homicide activity. Finally, the article suggests that the crack cocaine markets-gun availability linkage is highly plausible. Figures, tables, references