The aim of this research was to study the ontogenesis of black and white ruffed lemur Varecia variegata variegata vocalisations by comparing the signals emitted by a mother with those emitted by her offspring in order to estimate the relations between them. The lemurs live in captivity at "Parco Natura Viva'' in Pastrengo (VR-Italy), in a structure consisting of indoor and outdoor sections (cages are respectively of 3.00 x 3.00 m and 5.00 x 5.00 m). The studied group is formed by a pair and their offspring (a young female born in 1994 and one born in 1995; a male born in 1996). The vocalisations of the male (1996) and the female (1995) offspring were collected and analysed, starting from the first days of life until six and 18 months old. The vocalisations were recorded by analogue recorder Marantz CP 230 and DAT recorders Aiwa HD-SI, Sony TCD-D7, Aiwa PRO HS77; connected microphones were Sennheiser ME88 and ME66, Trevi ME-27 and Shure Studio 1.1. Vocalisations were analysed with a Macintosh IIci computer using Sound Designer IITM and Canary 1.1.1 programs and IBM compatible computer using a Voxys program suitable for providing the formants. The analysis has been focused on the "mew'', a low amplitude call emitted by new-borns as well as adults (Pereira et al. 1988). Preliminary results based on sequential analysis of behaviour preceding and following the "mews'' clearly show that the "mews'' are always emitted in a relaxed situation or social interaction. The "mews'' emitted by the young female are followed by the offspring approaching her mother only in 1.2% of cases and they elicit mother approaches in 13.0% of analysed sequences. The full description of sound characteristics is based on the description of spectrogram, spectrum and waveform plates. The tonal call exhibited 15-20 weak harmonic bands and a slow rise in pitch. The mean F0 of the 1995 female regularly decreases from the second day of life until the 166th day. From that time until 14 months old it varies from 230 to 232 Hz depending on the day. Her mother (5 years old) has a mean F0 of 232 + 13. The fundamental frequency and the first formants show the same trend. The mean call length tends to be shorter in the first days of life (range 112-582 msec) and 'becomes stable (700-800 msec) before the third month of life. Adult call length varies from 700 to 850 msec length. The amplitude pattern of the first 4 formants show a decreasing trend. The first one exhibits the highest amplitude also in new-borns. The energy distribution of the other formants becomes stable over the first 5 months of life.