8. Any two vertices of a cube determine a line, and among these lines, there are $\qquad$ pairs of lines that are perpendicular and skew.

Translating the text into English while preserving the original formatting and line breaks, the result is as above. Note that the blank space represented by $\qquad$ is kept as it is in the original text.
8. 78.

The lines determined by two vertices of a cube can be divided into three categories: 12 edges, 12 face diagonals, and 4 body diagonals, denoted as class $\mathrm{a}$, class $\mathrm{b}$, and class $\mathrm{c}$, respectively.

It is easy to see that each line of class $\mathrm{a}$ is perpendicular and skew to 4 lines of class $\mathrm{a}$, 2 lines of class $\mathrm{b}$, and 0 lines of class $\mathrm{c}$,

each line of class $\mathrm{b}$ is perpendicular and skew to 2 lines of class $\mathrm{a}$, 1 line of class $\mathrm{b}$, and 2 lines of class $\mathrm{c}$,

each line of class $\mathrm{c}$ is perpendicular and skew to 0 lines of class $\mathrm{a}$, 6 lines of class $\mathrm{b}$, and 0 lines of class $\mathrm{c}$.
$$
\begin{array}{l}
\text { There are a total of } 12(4+2+0)+12(2+1+2)+4(0+ \\
6+0)=156 \text { pairs. }
\end{array}
$$

Since each pair is counted twice, the number of line pairs is $156 \div 2=78$.