1. In this paper we shall give some moment and probability inequalities for the supremum of the arithmetic mean of random variables. These are in some special cases arbitrary but, in general, we shall restrict ourselves to the case of martingales or of totally independent random variables. By the aid of these inequalities we deduce some strong laws of large numbers.In the sequel we shall use the following results. Let So = 0, Si, S,, . . . be a martingale. In his paper [ 13 BURKHOLDER proved the following inequality : if p > 1 then there exist constants Cp and cp such that holds, where x k = X ks k -i , Ic = 1 , 2 , . . . is the martingale difference sequence. As a consequence, we obtain for p > 1 the famous inequality of MARCIN- KIEWICZ and ZYGMUND for totally independent random variables X , with E(X,) = 0, k = 1, 2, . . . In the latter case it is known that (1) holds also forFor 1 5 p 5 2 we obtain by the well-known C,-inequality that P n ~((~8x:)i) 2 i= c 1 E(lxilp) * Also, for p > 2 using the inequality of HOLDER we get Thus, if So = 0, S,, S,, . . . is a martingale, then for p > 1 we obtain by (1)with a constant Cp and with a = max 0, ~--1 . c 1 If p 5 1 and Xi, X,, . . . is an arbitrary sequence of random variables, then, as it is known, ( 2 ) holds by the C,-inequality.