Recent data suggest a simple and intriguing form of the neutrino mass matri
x. We show how the data may constrain solar neutrino oscillations to be nea
rly maximal [and rule out the small-angle Mikheyev-Smirnov-Wolfenstein (MSW
) explanation of solar neutrino observations] if relic neutrinos comprise a
t least three percent of the critical mass density of the universe.