Context :

Aims : The goal of this study is to measure parameters of the integrated H i emission for twenty-two dwarf galaxies with oxygen abundance 12+ \log ( O/H ) in the range of 7.42 to 7.65 , which are representatives of the eXtremely Metal-Deficient ( XMD ) galaxy group .
Some of them are expected to be similar to the well-known candidates for local young galaxies , I Zw 18 and SBS 0335 - 052 that have most of their baryon mass in the form of neutral gas .
Therefore , the H i 21-cm line observations are crucial to understanding their group and individual properties .

Methods : The Nançay Radio Telescope ( NRT ) with the upgraded focal receiver was used for observations of the 21-cm H i -line .
This permitted the detection of the faintest sources with rms of \sim 1 mJy per 10.5 km s ^ { -1 } resolution element .

Results : For eighteen detected galaxies we present the parameters of their integrated H i line emission and describe the data on individual objects in more detail .
For four undetected XMD galaxies , we give upper limits on their M ( H i ) .
For 70 % of the twenty studied non-LSB ( low surface brightness ) XMD galaxies , we find evidence ( both from H i and optical data ) for their interaction with neighboring objects .
In the brief discussion of the group H i properties of the observed subsample ( the total O/H range is of 0.23 dex , or a factor of 1.7 ) , we underline the broad distributions of the H i mass ( range is of 2 orders of magnitude ) , of the ratio M ( HI ) /L _ { B } ( of 1 order of magnitude ) , and of the blue luminosity ( range is of 2 orders of magnitude ) .
We also obtained H i parameters of six galaxies that do not belong to the XMD sample .
As a by-product , we have detected an H i -object with V _ { hel } = 188 km s ^ { -1 } , which is probably a part of a new high-velocity H i cloud ( HVC 234.3-16.8+208 ) near our Galaxy , in the direction of AM 0624–261 .

Conclusions : These data increase the number of XMD galaxies with known integrated H i parameters ( or upper limits ) by a factor of two .
This allows us to address statistical properties of this group , which will be presented in a forthcoming paper .