Major uncertainties of biological measurements in respect of parameters to which they are referred, cytochemical techniques, subcellular fractionation, light microscopy, electron microscopy, examination of cell membranes, dimensions of cells and intracellular movements, are discussed. The assumptions inherent in widely used techniques are noted and their warrant-ability examined. The impact of insufficient control experiments is shown to be considerable. A few important pieces of evidence in current generally accepted theories--mostly from neurobiology--are highlighted. All these problems represent incomplete experiments, from which it is premature to draw conclusions.