Experimental results about dislocation etch-pits on 100, 111, and 110 surfaces of electron beam floating zone-melted molybdenum single crystals are described. Electrolytic etching reagents used in this work are mixtures of methyl alcohol, sulphuric acid, and chloric acid. Besides, etch-lines arranged in parallel sets and hexagonal networks are observed on 111 and 110 surfaces, these are interpreted as etch-figures of dislocation lines.An empirical rule for the interpretation of etch-figures of dislocation lines is deduced from observations. Observed etch-figures are projections on observation plane of dislocation lines in the etched layer, its widths depend on the distance between dislocation line-elements and original surface, so that an exaggerated perspective effect is obtained. Hence the arrangements of dislocation lines in space may be deduced directly from observed etch-figures. By means of multiple etching technique, some examples of dislocation arrangements in space are presented.Correspondance between etch-pits and sites of dislocation lines intersecting original surface has been studied. In general, such correspondance is observed by means of an etching-polishing-reetching technique. However, experimental results show that such correspondance may be violated in some cases. For instance, when the angle between a dislocation line and observation plane is less than a critical value (15°-24°), no etch-pit is observed. On the other hand, nodes of dislocation networks after prolonged etching, may be revealed as arrays of etch-pits. The significances of these results on the interpretation of etch-pits figures are discussed.The etch-figure method has been compared with other methods of direct observation of dislocation lines, its merits and demerits are discussed, and it is concluded that the etch-figure methods is superior to all other existing methods in the study of dislocations in metal crystals when the dislocation density is within the range from 104 to 108 cm-2.