Fluorescence excitation spectra of small and dilute samples of solid s
olutions at helium temperatures show the spectrally resolved lines of
single solute molecules. The signal-to-noise ratio is sufficient for s
everal spectroscopic and time-correlated experiments, which are briefl
y reviewed here. In particular, paramagnetic resonance within the trip
let manifold was demonstrated recently for single pentacene molecules
in a p-terphenyl crystal.