Problems of tunneling spectroscopy are discussed for TiO2, various tips and environments. Calibration measurements on gold surfaces with Au, Ti and W tips in dry nitrogen and air respectively show possible artefacts. Reversible, linear VT- and DT-spectra were obtained only in dry nitrogen. Measurements in air or with oxide covered tips, eg Ti, are ill-defined and suffer from changes in the tunneling system. VT-spectra of oxide covered titanium as a substrate with Au-tips in dry nitrogen strongly depend on the oxide thickness. The inverse system Au (substrate)/Ti-tip gives spectra similar to ultrathin oxide films on titanium with a gold tip. DTS measurements indicate a penetration of the tip into the oxide. The correlation between obtained symmetric gaps and the unsymmetric band gap of the n-type semiconductor TiO2 is questioned. The unexpected influence of the U(t) scan type proves-that modifications of TiO2 cannot be excluded even in dry nitrogen. Detected modifications in wet air may be useful, however, for nanotechnology.