Cyclotron instabilities in a thermally anisotropic hydrogen plasma due to resonant particles laying near the peak of their distribution functions are obtained in two cases. In the first case both protons and electrons have resonant particles near the peak of their distribution functions. The instabilities are found to be driven by both proton and electron thermal anisotropy of the resonant particles. In the second case only electron component has resonant particles near the peak of its distribution function. The instabilities are found to be driven by thermal anisotropy of the resonant electrons. Possible application to the interplanetary medium are briefly discussed.