Gas-phase reaction rate constants have been determined over the temperature range 295-436 K for the reactions of germylene, GeH2, with acetylene (GeH2 addition across a triple bond), trimethylsilane (GeH2 insertion into a Si-H bond), and phenylgermane. The room-temperature rate constant for germylene reacting with benzene has been measured and is found to be a factor of similar to 300 smaller than that for phenylgermane, indicating that the latter reacts by GeH2 insertion into the Ge-H bonds. A negative temperature dependence is observed in all cases. The activation energies, obtained from weighted linear fits to the data over the experimental temperature range, are - 3.5 +/- 0.3, -11.0 +/- 0.4, and - 3.6 +/- 0.3 kJ mol(-1) for acetylene, trimethylsilane, and phenylgermane, respectively, while the respective frequency factors, log( A/cm(3) molecule(-1) s(-1)), are - 10.5 +/-0.1, - 11.8 +/- 0.1, - 10.1 +/- 0.1.