The work comments on the essay by M. Klein ‘On the Sense of Loneliness’, also in the light of some previously unpublished documents on this topic held by the Melanie Klein Trust Archive (see Milton, 2018). The Author analyses the text, framing it in the evolution of M. Klein's thought starting from the second half of the Forties, highlighting some important transformations: the importance attributed to the establishment of an early relationship of intimacy with the mother through a direct contact of preverbal comprehension, preceding the mechanism of splitting, the communicative function of «normal» projective identification; the relationship between sense of loneliness and integration; the instability and the intrinsic incompleteness of the integration processes.

KEY WORDS: Integration processes, Melanie Klein, pre-verbal comprehension, projective identification, sense of loneliness.