  The spectra of the QSOs PKS2126-158 ($z_{em}=3.27$) and Q0055-269
($z_{em}=3.66$) have been observed at high resolution ($2.2 - 2.7 \times
10^4$). Significant clustering, with $\xi \simeq 1$ at $\Delta v=100$ km
s$^{-1}$, is detected in both cases for lines with $\log N_{HI} \geq 13.8$. A
similar result is obtained analysing the data available in the literature for
Q0014+81. An anticlustering signal is also detected on scales $\Delta v \sim
600$ km s$^{-1}$. Two voids of size $\sim 2000$ km s$^{-1}$ are found in the
spectrum of Q0055-269 with a probability of $2\times 10^{-4}$.
