$echantillonM="";
		foreach($_POST['ech-remis'] as $v)
		   $echantillonM.=$v."/";

$_POST['ech-remis'] est un tableau et nom une chaîne de caractère !


@+

 <?php
include( 'connexion.php' ); 
<form method="post" action="enregisterV.php">
<table width="1399" border="0">
  <tr>
<th width="144" height="26" bgcolor="#FFFFCC" ><span class="style14 style6">Medecin</span></th>
<th width="25" bgcolor="#FFFFCC"> <span class="style14 style6">ech-remis</span></th>
</tr>		
<td width="62">
			<select name="nom" class="style14" id="nom">
										<option selected="selected" value="">Selectionnez :</option>
										<option value="Oui">Oui</option>
										<option value="Non">Non</option>
										<option value="Autre">Autre</option>
		</select>
</td>
        <td width="62">
           <select multiple name="ech-remis[]" id="ech-remis" class="style14" >
										<option selected="selected" value="">Selectionnez :</option>
										<option value="Maxi_G ">Maxi G </option>
										<option value="Maxi_20">Maxi 20</option>
										<option value="Trivimag">Trivimag </option>
										<option value="Biosept">Biosept</option>
										<option value="Hepanat">Hepanat </option>
										<option value="Dornat_Plus">Dornat Plus</option>
										<option value="Panax_Effervescent">Panax Effervescent </option>
										<option value="Extraform_Sirop">Extraform Sirop</option>
										<option value="Erbaven">Erbaven</option>
										<option value="Centelys">Centelys</option>
		  </select></td>
      
	</tr>
</table>

<table width="1110" align="center" cellpadding="3">
  <tr align="right" valign="top">
    <th width="668" height="30" scope="row">&nbsp;</th>
    <td width="653">&nbsp;</td>
  </tr>
  <tr align="right" valign="top">
<th width="355" height="30" scope="row"><label>
<input name="enregistrer" class="Style1" value="Enregistrer" style="width: 25%" type="submit" />
</label>  
</th>
<td width="358"><div align="left">
<input name="reset" type="reset" id="submit" value="vider" class="Style1" style="width: 25%"/>
</div></td>
</tr>
</table>
</form>

<?php session_start() ;
ob_start();
include( 'connexion.php' );
$m=$_POST['nom'];
$n=$_POST['ech-remis'];
$z=mysql_query('insert into 
 visiter values 
 ("","'.addslashes($m).'","'.addslashes($n).'")') or die(mysql_error());
 //echo " bien enregistrée";
 header('Location: ll.php') ;

<select name="echantiollon[]" id="remis" class="style14" multiple >
<option selected="selected" value="">Selectionnez </option>
<option value="a">a </option>
<option value="b">b</option>
<option value="c">c</option>
 </select>